How to Boost Your Email Efficiency With SMTP Send Email Protocol
How to Boost Your Email Efficiency With SMTP Send Email Protocol
How to Boost Your Email Efficiency With SMTP Send Email Protocol
Jan 23, 2025
Sending cold outreach emails can feel like a shot in the dark. You find the right prospects, craft the perfect message, and hit send, only to find that your email ended up in the depths of the spam folder—if it even got delivered. Implementing an SMTP Send Email strategy can help ensure your emails get delivered quickly and reliably by optimizing the sending process. In this blog, we'll explore the ins and outs of SMTP Send Email, revealing how it works and how cold emails tips can help you streamline your email-sending process for faster, more reliable communication.
One valuable tool for implementing an SMTP strategy is Inframail's email infrastructure. This solution helps optimize your email deliverability to boost your cold outreach success.
Table of Contents
What is SMTP (And What Does SMTP Stand For)?
What happens behind the scenes when you hit "Send" on an email? Enter SMTP—the Simple Mail Transfer Protocol. The silent workhorse ensures your messages travel across the vast expanse of the internet and land in the right inbox.
SMTP stands for Simple Mail Transfer Protocol—an application mail server that sends, receives, and relays outgoing emails between senders and receivers. SMTP is the protocol that allows you to send and receive emails. It is the technology behind email communication, and without it, email communication would be nonexistent since SMTP determines which servers will receive your relay messages.
The Simple Mail Transfer Protocol That Powers Email Communication
S = Simple: SMTP is designed to be straightforward to implement.
M = Mail: SMTP is built to send email messages across networks.
T = Transfer: SMTP transfers email messages from one server to another.
P = Protocol: SMTP is a set of rules (or protocols) that lets different email systems and servers communicate with each other.
SMTP is the digital postal service of the internet. It determines which servers will receive your messages and how they'll get there. Without SMTP, your emails would be like letters without addresses—they'd have nowhere to go.
What Does SMTP Do (and Not Do)?
As the “T” in its name indicates, SMTP is a transport protocol: It moves messages from point A to point B. Like many other Internet protocols, SMTP is intended to be used with the Transmission Control Protocol (TCP), which guarantees reliable delivery of the individual packets that make up a conversation.
Role and Limitations: Deliverability, Tracking, and Beyond
Using IP means that we can depend on SMTP to send the message contents to a server eventually, but what happens to it after that is up to the server? Imagine what happens when a delivery driver leaves a package at your office on a Saturday. What happens to it after delivery isn’t his problem.
Examples of services that SMTP doesn’t necessarily provide but are still very valuable are:
Deliverability
Monitoring
Tracking
Authentication
Encryption
What is an Email Server—and What Is an SMTP Server?
An outgoing mail server is a generalized term to describe a system that collects, processes, and serves email. Much like a mail carrier, every email message passes through the mail server before reaching its destination. Without servers, you could only send emails to people whose addresses matched your domain—Gmail.com to Gmail.com, for instance.
Because an SMTP email server pertains to outgoing email, it’ll have an address (or addresses) that the mail client or application you use can set that generally looks like this: smtp.serveraddress.com. For example, the SMTP server Gmail uses is smtp.gmail.com, and Twilio SendGrid’s is smtp.sendgrid.com. You can usually find your SMTP email server address in your mail client’s account or settings section.
How SMTP’s Store and Forward Process Ensures Reliable Email Delivery Across Networks
Using a store and forward process, SMTP works with the mail transfer agent to move your email across networks to the correct computer and email inbox. So when you send an email with SMTP host Gmail or AOL, the SMTP server processes your email, decides which server to send the message to, and relays the message to that email server. The recipient’s inbox service provider, such as Gmail or AOL, then downloads the message and places it in the recipient’s inbox. Our docs page provides more details to help you understand the meaning of SMTP.
What is an SMTP Email Service?
SMTP email services handle all the SMTP protocol details for you. They're email service providers (like Twilio SendGrid) that do all the behind-the-scenes work to get your emails adequately formatted, sent, and delivered to the recipient's mail server.
An SMTP email service manages your complex infrastructure. It does everything from:
Improving email deliverability
Securing sent emails
Providing valuable email performance analytics
Common SMTP server providers and settings
SMTP: Provider URL SMTP Settings
AOL: aol.com smtp.aol.com
AT&T: att.net smtp.mail.att.net
Comcast: comcast.net smtp.comcast.net
iCloud: icloud.com/mail smtp.mail.me.com
Gmail: gmail.com smtp.gmail.com
Outlook: outlook.com smtp-mail.outlook.com
Yahoo!: mail.yahoo.com smtp.mail.yahoo.com
How They Differ from Standard Servers
Is an SMTP server the same as a standard server? Like most servers, the SMTP server processes data sent to another server, but it has the specific purpose of processing data related to the sending and relaying of emails. An SMTP server is not necessarily on a machine but can be an application constantly running in anticipation of sending new mail.
Why are SMTP Servers Important?
When communicating over email, it's crucial to send email to your recipient safely and on time. Your email can’t reach its destination without an SMTP server. Once you hit Send, the email transforms into a string of code sent to the SMTP server, which processes that code to pass the message. Without the SMTP server to process the message, the message wouldn’t translate.
How SMTP Servers Verify Accounts and Handle Undeliverable Emails
The SMTP server verifies that the outgoing email is from an active account. In other words, the email server checks whether an active or working email account sent the outgoing message, protecting your inbox from illegitimate emails. If the email is undeliverable, the SMTP ensures the email will bounce back to the sender, letting them know they have an incorrect email address or the receiving email server blocked the email for whatever reason.
Related Reading
• How to Send Bulk Emails
• Outreach Automation
• How to Know if Someone Opened Your Email
• How to Send a Cold Email for Networking
• How to Follow Up on a Cold Email
• Best Time to Send Cold Emails
How Does SMTP Send Mail?
Here's how it works step-by-step:
The Sender Writes an Email: Open your email client (like Gmail or Outlook), type your message, and click "send."
The Mail Client Sends the Email: Your email client connects to an SMTP server and sends your email to the server using the "MAIL FROM" and "RCPT TO" commands.
The SMTP Server Takes Over: The SMTP server acts as the mail carrier for your email, delivering it securely to the recipient’s server. It checks the recipient's domain (e.g., yahoo.com) to determine where to send it. If the recipient's domain matches the sender's, the email goes directly to the mail server.
Mail Transfer Agent (MTA) Finds the Recipient’s Server: If the email is for a different domain, the SMTP server connects to the recipient's mail server. The SMTP server uses DNS (Domain Name System) to locate the recipient's email server.
The Recipient’s Mail Server Receives the Email: The mail is delivered to the recipient's inbox. The mail delivery agent works with SMTP servers to securely deliver emails to the recipient’s inbox. This process includes filtering for spam or other security checks.
The Recipient Reads the Email: The email client (like Yahoo Mail or Outlook) retrieves the message and displays it for the recipient to read.
Types of SMTP Servers
Dedicated SMTP Server: Exclusively used by a single organization or user. Ensures high reliability and speed for email delivery. It is ideal for businesses with high email volumes.
Shared SMTP Server: Multiple users share the server resources. This is cost-effective for small businesses or low email volumes. However, due to shared usage, occasional delays may occur.
Cloud-Based SMTP Server: Hosted on cloud platforms for scalability. Offers high availability and easy integration with web applications. Examples: AWS SES, SendGrid, or Google Workspace.
ISP SMTP Server: Provided by Internet Service Providers to their customers, this server is simple for personal use but limited to business needs. It often comes with restrictions like email volume caps.
Transactional SMTP Server: Designed to handle automated, real-time messages (e.g., order confirmations, password resets). Ensures quick delivery and detailed analytics. Widely used in e-commerce and SaaS platforms.
Relay SMTP Server: This server acts as an intermediary, forwarding emails from one server to the recipient’s server. It is helpful for bypassing restrictions on local SMTP servers and is commonly used in hybrid systems. Relay servers are critical for email delivery across different mail servers and networks.
Internal SMTP Server: This server operates within an organization’s private network. It is secure, controlled, and suitable for sensitive communications. It requires in-house maintenance and expertise.
Open SMTP Server: This server accepts email delivery from any sender without authentication. It is rarely used today due to its vulnerability to spam and misuse. Although it was historically popular, it is now discouraged for security reasons.
Step-by-Step Guide to Setting Up an SMTP Server
Setting up an SMTP server might sound technical, but it's easier than you think. Follow these simple steps to get your email system running smoothly.
1. Choose Your SMTP Server
Decide whether you’ll use your ISP’s SMTP server, a cloud-based SMTP server, or set up your own. Popular options include:
Google Workspace
Email provider’s SMTP service
2. Install Necessary Software
For Windows: Use built-in features like the IIS SMTP server.
For Linux: Install software like Postfix or Sendmail.
Use commands such as:
`sudo apt-get update`
`sudo apt-get install postfix`
3. Configure the SMTP Server
Open your SMTP server settings.
Set the domain name (e.g., example.com) and outgoing mail server (smtp.example.com).
Configure the SMTP port (commonly 587 for TLS or 465 for SSL).
4. Set Up Authentication
Enable SMTP authentication to prevent unauthorized access.
Create a username and password for secure connections.
5. Test Your SMTP Server
Use command-line tools like Telnet or PowerShell for testing. For example: `telnet smtp.example.com 587` Send a test email to ensure everything works.
6. Enable Security Protocols
Configure TLS (Transport Layer Security) or SSL (Secure Sockets Layer) for encrypted communication. This ensures that your emails are safe during transit.
7. Integrate with Email Clients
Add your SMTP server details to your email client (like Outlook, Gmail, or Thunderbird).
Use settings such as:
SMTP Server: smtp.example.com
Port: 587 (TLS) or 465 (SSL)
Username: Your email address
Password: The password you created
8. Monitor and Troubleshoot
Check email logs regularly to identify issues. Use tools like delivery status notifications (DSNs) to track email performance.
SMTP Commands You Need to Know
1. HELO/EHLO
Used to introduce the client to the SMTP server. HELO is the older version; EHLO is its extended version, enabling modern SMTP features.
Example: EHLO mail.example.com
2. MAIL FROM
Specifies the sender’s email address. Begin the email transaction process.
Example: MAIL FROM:<sender@example.com>
3. RCPT TO
Identifies the recipient’s email address. It can be used multiple times to send emails to numerous recipients.
Example: RCPT TO:<recipient@example.com>
4. DATA
This signal tells the server the client is ready to send the email content. The email body follows this command, ending with a period on a new line (.).
Example: DATA Subject: Test Email This is a test email. Message contents, including text and attachments, are formatted and transmitted by the SMTP protocol.
5. QUIT
Terminates the SMTP session gracefully. Ensures that the server properly logs the session.
Example: QUIT
6. AUTH
Used for client authentication on the SMTP server. Supports different authentication methods like:
PLAIN
LOGIN
Example: AUTH LOGIN
7. STARTTLS
Initiates encryption for secure communication. Often used before sending sensitive email content.
Example: STARTTLS
8. RSET
Resets the current session without closing the connection. This is useful for correcting errors during email transmission.
Example: RSET. Other SMTP commands, like VRFY and NOOP, offer additional functionalities for debugging and testing.
9. VRFY
Verifies if a specific email address exists on the server. It is rarely used due to security and privacy concerns.
Example: VRFY user@example.com
10. NOOP
Sends a ping-like request to keep the connection alive without doing anything. Useful for maintaining long sessions.
Example: NOOP
Related Reading
• How Many Cold Emails Per Day
• Mailchimp for Cold Emails
• Best Bulk Email Sender
• Best Email Outreach Tools
• Bulk Email Providers
• Best Business Email Providers
• Best SMTP Server
• AI Tools for Email Marketing
• Amazon Ses Alternatives
• Postfix vs Sendmail
• Amazon Ses vs Sendgrid
Role of Mail Transfer Agent (MTA) in SMTP: Ensuring Efficient Email Routing
The Mail Transfer Agent (MTA) plays a crucial role in the Simple Mail Transfer Protocol (SMTP). It is the delivery driver for your emails, ensuring they reach the correct destination. A Mail Submission Agent (MSA) ensures that all outgoing mail relay messages are correctly formatted and delivered to the SMTP server. When you hit Send, the MTA transfers your message from the sender’s email client to the recipient’s mail server. Without the MTA, emails would have no way of navigating the complex paths of the internet to reach the intended inbox.
How the Mail Transfer Agent (MTA) Ensures Accurate and Efficient Email Routing
Here’s how the MTA works:
It receives the email from the SMTP server.
Then, it determines the recipient’s mail server using the Domain Name System (DNS), which matches the recipient’s domain to its mail server.
The MTA transfers the recipient's email addresses to the recipient's server for delivery.
This process ensures that emails are routed accurately and efficiently, even when they pass through multiple servers.
How to Set Up Gmail SMTP for Seamless Email Sending
1. Enable Gmail SMTP Access
Log into your Gmail account.
Go to Settings > See All Settings > Forwarding and POP/IMAP.
Enable IMAP Access and click Save Changes.
2. Generate an App Password
Visit your Google account's Security section.
If 2-step verification is not already enabled, turn it on.
Under "App Passwords," generate a unique password for SMTP access.
Use this password in the next steps.
3. SMTP Server Details
Use the following details for setup:
SMTP Server: smtp.gmail.com Port: 587 (for TLS) or 465 (for SSL)
Username: Your Gmail address (e.g., yourname@gmail.com)
Password: The App Password generated earlier.
4. Set Up in Email Clients or Application
Open your email client or application (e.g., Outlook, Thunderbird).
Add your Gmail account details.
Enter the SMTP server details from the previous step.
5. Test the Configuration
Send a test email to check if the setup works.
Double-check the port, server, and password settings if the email isn’t sent.
6. Troubleshooting Common Issues
Authentication Error: Ensure you're using the correct App Password.
Blocked Access: Check if Gmail flagged suspicious activity.
Firewall Issues: Confirm your network isn't blocking SMTP ports.
7. Advanced Configuration for Applications
For advanced integration, use tools like Postfix, PHPMailer, or Nodemailer.
Include your Gmail SMTP settings in the configuration file to automate email sending.
How to Address SMTP Error Codes
SMTP error codes are messages the mail server sends to explain why an email wasn’t delivered. They typically look like three-digit numbers (e.g., 550 or 421). Each number provides specific details about the issue.
Common SMTP Error Codes and What They Mean
550: Requested action not taken: The recipient's mail server rejected your email. It could be due to spam filters or a nonexistent email address.
421: Service not available: This occurs when the recipient’s server is temporarily unavailable.
451: Local error in processing: The sender’s email server encountered a temporary problem.
554: Transaction failed: The email was rejected because it was flagged as spam or contained errors.
How to Fix SMTP Errors
Check the Recipient’s Email Address: Ensure the email address is typed correctly. Even a small typo can cause errors like 550.
Review Your Email Content: If flagged as spam, remove suspicious links, large attachments, or repetitive keywords.
Retry Sending Later: Try again after some time for temporary errors like 421 or 451. Servers often resolve these issues quickly.
Update Your SMTP Settings: Confirm your SMTP server address, port, and authentication details are correct.
Contact the Server Administrator: If the error persists, contact the email provider or server admin for assistance.
How to Set Up an SMTP Server on Windows/Linux
Setting up an SMTP server on Windows or Linux systems and configuring one for web applications involves administrative rights and a basic understanding of your network and server environment.
Below, we'll go through the processes for both environments.
SMTP Server on Windows
For Windows Server (e.g., Windows Server 2019):
Install the SMTP Server Feature: Open the Server Manager. Go to "Manage" -> "Add Roles and Features". Navigate the wizard and select "SMTP Server" under the "Features" section.
Configure SMTP Service: After installation, open the Internet Information Services (IIS) 6.0 Manager (note: SMTP is managed through IIS 6.0 Manager even on newer servers). Right-click on "SMTP Virtual Server #1" -> "Properties". Configure general settings (e.g., IP address, port (usually port 25), and limits).
Set Up SMTP Email: Under "Access" tab, configure connection and relay restrictions. Under "Delivery" tab, configure outbound connections, advanced delivery options including smart host settings if you are relaying emails through an external SMTP server.
Secure Your SMTP Server: Restricting relay to prevent spam is crucial. Only allow your server IP or specific IP addresses to relay emails. Consider enabling TLS for secure email transmission.
Test Your SMTP Server: Use telnet or PowerShell (Send-MailMessage cmdlet) to send a test email and verify that your SMTP server works correctly.
SMTP Server on Linux
For Linux (e.g., using Postfix on Ubuntu):
Install Postfix: Run `sudo apt-get update` followed by `sudo apt-get install postfix`. During installation, you will be prompted to choose a configuration. For most users, "Internet Site" is appropriate.
Configure Postfix: Edit the main configuration file (/etc/postfix/main.cf) to set up domain, IP, and other settings. If applicable, specify myhostname, mydomain, myorigin, and relay host (relayhost).
Control Access and Relay: Edit /etc/postfix/main.cf to set up mynetworks (IP addresses allowed to send emails) and adjust relay controls.
Enable and Start Postfix: Run `sudo systemctl enable postfix` and `sudo systemctl start postfix` to enable and start Postfix automatically.
Test Your SMTP Server: Use commands like telnet or sendmail for basic email-sending tests to ensure the SMTP server is operational.
Send Emails with SMTP in Python
Python provides the smtplib library, which defines an SMTP client session object that can send mail to any Internet machine with an SMTP or ESMTP listener daemon. python
import smtplib
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
SMTP server configuration
smtp_server = "smtp.example.com"
port = 587 # For starttls
sender_email = "your-email@example.com"
password = "your-password"
receiver_email = "receiver@example.com"
Create the email message
message = MIMEMultipart("alternative")
message["Subject"] = "Test Email"
message["From"] = sender_email
message["To"] = receiver_email
Create the plain-text and HTML version of your message
text = """\
Hi,
This is a test email sent from Python."""
html = """\
<html>
<body>
<p>Hi,<br>
This is a <b>test email</b> sent from <i>Python</i>.
</p>
</body>
</html>
Attach parts into message container
part1 = MIMEText(text, "plain")
part2 = MIMEText(html, "html")
message.attach(part1)
message.attach(part2)
# Send the email
try:
server = smtplib.SMTP(smtp_server,port)
server.starttls() # Secure the connection
server.login(sender_email, password)
server.sendmail(sender_email, receiver_email, message.as_string())
finally:
server.quit()
Send Emails with SMTP in Java
The JavaMail API can send emails via SMTP. To use it, you need to include the JavaMail dependency in your project. java
import javax.mail.*;
import javax.mail.internet.*;
import java.util.Properties;
public class SendEmail {
public static void main(String[] args) {
String host = "smtp.example.com";
String user = "your-email@example.com";
String pass = "your-password";
String to = "receiver@example.com";
String subject = "Test Email";
String messageText = "This is a test email sent from Java.";
Properties props = System.getProperties();
props.put("mail.smtp.host", host);
props.put("mail.smtp.user", user);
props.put("mail.smtp.password", pass);
props.put("mail.smtp.port", "587");
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.starttls.enable", "true");
Session session = Session.getDefaultInstance(props, null);
MimeMessage message = new MimeMessage(session);
try {
message.setFrom(new InternetAddress(user));
message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
message.setSubject(subject);
message.setText(messageText);
Transport transport = session.getTransport("smtp");
transport.connect(host, user, pass);
transport.sendMessage(message, message.getAllRecipients());
transport.close();
} catch (MessagingException me) {
me.printStackTrace();
}
}
}
Send Emails with SMTP in Node.js
Node.js allows sending emails using SMTP with the help of the nodemailer module.
Install nodemailer using npm:
`npm install nodemailer`
Then, use the following code to send an email: javascript
const nodemailer = require('nodemailer');
let transporter = nodemailer.createTransport({
host: "smtp.example.com",
port: 587,
secure: false, // true for 465, false for other ports
auth: {
user: "your-email@example.com",
pass: "your-password",
},
});
let mailOptions = {
from: '"Sender Name" <your-email@example.com>',
to: "receiver@example.com",
subject: "Test Email",
text: "This is a test email sent from Node.js.",
html: "<b>This is a test email sent from Node.js.</b>",
};
transporter.sendMail(mailOptions, (error, info) => {
if (error) {
return console.log(error);
}
console.log('Message sent: %s', info.messageId);
});
How to Integrate SMTP with WordPress
Integrating SMTP (Simple Mail Transfer Protocol) with WordPress ensures that your website's emails are reliably sent through a professional mail server, significantly reducing the chances of your emails being marked as spam.
Here’s a step-by-step guide on how to set up SMTP in WordPress:
1. Choose an SMTP Plugin
WordPress does not natively support SMTP email configuration, so you must use a plugin. Several other SMTP email server plugins are available, but one of the most popular and user-friendly is "WP Mail SMTP" by WPForms.
How to:
Go to your WordPress dashboard.
Navigate to "Plugins" > "Add New".
Search for "WP Mail SMTP".
Click "Install Now" on the plugin, then activate it.
2. Configure the SMTP Plugin
After activating the plugin, configure it with your SMTP service providers' details.
How to:
In your WordPress dashboard, go to "WP Mail SMTP" > "Settings.”
The “From Email” and “From Name” options are here. The "From Email" should be the email address you want to send emails from, and it's recommended that this address be valid on your domain to improve deliverability.
Check the box that says “Set the return path to match the From Email" to ensure bounce messages are sent to the From Email address.
3. Choose Your SMTP Mailer
WP Mail SMTP allows you to choose from several free SMTP, email servers, and services, including:
Default SMTP
Sendinblue SMTP
Mailgun SMTP
SendGrid SMTP
Gmail SMTP (for Gmail or G Suite accounts)
Microsoft SMTP (Outlook.com and Office 365)
Amazon SES SMTP
Other SMTP
Select the mailer that best suits the same email domain and your needs. If you have an SMTP email server address, choose “Other SMTP.”
4. Enter Your SMTP Settings
If you selected "Other SMTP,” you must enter your own SMTP server name details.
These details typically include:
SMTP Host: The address of your SMTP server.
SMTP Port: Common ports include 587 (recommended for TLS encryption) and 465 (SSL encryption).
Encryption: Choose between SSL and TLS encryption. TLS is recommended if your SMTP server supports it.
Authentication: Enable authentication and enter the SMTP username and password provided by your SMTP service or hosting provider.
For other mailers, you will be prompted to enter API keys or OAuth credentials, which you can get from your email service provider's dashboard.
5. Test Your SMTP Settings
WP Mail SMTP provides an option to send a test email.
How to:
Navigate to "WP Mail SMTP" > "Email Test" in your WordPress dashboard.
Enter an email address where you want to receive the test email and click "Send Email.”
You should receive the test email confirming that your SMTP settings are correctly configured.
6. Save Your Settings
After successfully sending a test email, ensure all your settings are saved. Your WordPress site is configured to send emails using SMTP, improving email deliverability.
Start Buying Domains Now and Setup Your Email Infrastructure Today
Cold outreach is a tricky thing. You have to go through the spam folder to get a chance to connect with your prospects. Then, you must write an engaging email that compels your reader to act. The last thing you want to worry about in your cold outreach strategy is your email infrastructure. That’s why I recommend Inframails SMTP email infrastructure to all my clients. Inframail takes the headache out of cold emailing with unlimited Microsoft-backed inboxes for a single flat rate. The boost your cold outreach will get by using Inframails email infrastructure will make your emails more reliable and improve deliverability, so you can connect with more prospects and grow your business.
Simplifying Cold Outreach
Inframail allows scaling their outreach efforts efficiently without the technical headaches of traditional providers like:
Agencies
Recruiters
Sales development representatives (SDRs).
Features like automated SPF, DKIM, and DMARC setup will save you hours of technical setup time, while dedicated email servers for each user ensure you get the best performance for your cold outreach. With 16-hour priority support daily, you can even get help with your email infrastructure while you sleep.
How Inframail Empowers Agencies, Recruiters, and SDRs to Scale Outreach Without Technical Hassles
Forget traditional cold email providers that charge per inbox and leave you wrestling with technical configurations. Inframail streamlines the entire process. We handle the complex infrastructure setup while you focus on reaching more prospects.
InfraMail provides the robust email infrastructure you need without the usual technical headaches and per-inbox costs, whether you're:
An agency looking to scale outreach
A recruiter connecting with candidates
An SDR driving sales
Start buying domains now and set up your email infrastructure today with our email infrastructure tool.
Sending cold outreach emails can feel like a shot in the dark. You find the right prospects, craft the perfect message, and hit send, only to find that your email ended up in the depths of the spam folder—if it even got delivered. Implementing an SMTP Send Email strategy can help ensure your emails get delivered quickly and reliably by optimizing the sending process. In this blog, we'll explore the ins and outs of SMTP Send Email, revealing how it works and how cold emails tips can help you streamline your email-sending process for faster, more reliable communication.
One valuable tool for implementing an SMTP strategy is Inframail's email infrastructure. This solution helps optimize your email deliverability to boost your cold outreach success.
Table of Contents
What is SMTP (And What Does SMTP Stand For)?
What happens behind the scenes when you hit "Send" on an email? Enter SMTP—the Simple Mail Transfer Protocol. The silent workhorse ensures your messages travel across the vast expanse of the internet and land in the right inbox.
SMTP stands for Simple Mail Transfer Protocol—an application mail server that sends, receives, and relays outgoing emails between senders and receivers. SMTP is the protocol that allows you to send and receive emails. It is the technology behind email communication, and without it, email communication would be nonexistent since SMTP determines which servers will receive your relay messages.
The Simple Mail Transfer Protocol That Powers Email Communication
S = Simple: SMTP is designed to be straightforward to implement.
M = Mail: SMTP is built to send email messages across networks.
T = Transfer: SMTP transfers email messages from one server to another.
P = Protocol: SMTP is a set of rules (or protocols) that lets different email systems and servers communicate with each other.
SMTP is the digital postal service of the internet. It determines which servers will receive your messages and how they'll get there. Without SMTP, your emails would be like letters without addresses—they'd have nowhere to go.
What Does SMTP Do (and Not Do)?
As the “T” in its name indicates, SMTP is a transport protocol: It moves messages from point A to point B. Like many other Internet protocols, SMTP is intended to be used with the Transmission Control Protocol (TCP), which guarantees reliable delivery of the individual packets that make up a conversation.
Role and Limitations: Deliverability, Tracking, and Beyond
Using IP means that we can depend on SMTP to send the message contents to a server eventually, but what happens to it after that is up to the server? Imagine what happens when a delivery driver leaves a package at your office on a Saturday. What happens to it after delivery isn’t his problem.
Examples of services that SMTP doesn’t necessarily provide but are still very valuable are:
Deliverability
Monitoring
Tracking
Authentication
Encryption
What is an Email Server—and What Is an SMTP Server?
An outgoing mail server is a generalized term to describe a system that collects, processes, and serves email. Much like a mail carrier, every email message passes through the mail server before reaching its destination. Without servers, you could only send emails to people whose addresses matched your domain—Gmail.com to Gmail.com, for instance.
Because an SMTP email server pertains to outgoing email, it’ll have an address (or addresses) that the mail client or application you use can set that generally looks like this: smtp.serveraddress.com. For example, the SMTP server Gmail uses is smtp.gmail.com, and Twilio SendGrid’s is smtp.sendgrid.com. You can usually find your SMTP email server address in your mail client’s account or settings section.
How SMTP’s Store and Forward Process Ensures Reliable Email Delivery Across Networks
Using a store and forward process, SMTP works with the mail transfer agent to move your email across networks to the correct computer and email inbox. So when you send an email with SMTP host Gmail or AOL, the SMTP server processes your email, decides which server to send the message to, and relays the message to that email server. The recipient’s inbox service provider, such as Gmail or AOL, then downloads the message and places it in the recipient’s inbox. Our docs page provides more details to help you understand the meaning of SMTP.
What is an SMTP Email Service?
SMTP email services handle all the SMTP protocol details for you. They're email service providers (like Twilio SendGrid) that do all the behind-the-scenes work to get your emails adequately formatted, sent, and delivered to the recipient's mail server.
An SMTP email service manages your complex infrastructure. It does everything from:
Improving email deliverability
Securing sent emails
Providing valuable email performance analytics
Common SMTP server providers and settings
SMTP: Provider URL SMTP Settings
AOL: aol.com smtp.aol.com
AT&T: att.net smtp.mail.att.net
Comcast: comcast.net smtp.comcast.net
iCloud: icloud.com/mail smtp.mail.me.com
Gmail: gmail.com smtp.gmail.com
Outlook: outlook.com smtp-mail.outlook.com
Yahoo!: mail.yahoo.com smtp.mail.yahoo.com
How They Differ from Standard Servers
Is an SMTP server the same as a standard server? Like most servers, the SMTP server processes data sent to another server, but it has the specific purpose of processing data related to the sending and relaying of emails. An SMTP server is not necessarily on a machine but can be an application constantly running in anticipation of sending new mail.
Why are SMTP Servers Important?
When communicating over email, it's crucial to send email to your recipient safely and on time. Your email can’t reach its destination without an SMTP server. Once you hit Send, the email transforms into a string of code sent to the SMTP server, which processes that code to pass the message. Without the SMTP server to process the message, the message wouldn’t translate.
How SMTP Servers Verify Accounts and Handle Undeliverable Emails
The SMTP server verifies that the outgoing email is from an active account. In other words, the email server checks whether an active or working email account sent the outgoing message, protecting your inbox from illegitimate emails. If the email is undeliverable, the SMTP ensures the email will bounce back to the sender, letting them know they have an incorrect email address or the receiving email server blocked the email for whatever reason.
Related Reading
• How to Send Bulk Emails
• Outreach Automation
• How to Know if Someone Opened Your Email
• How to Send a Cold Email for Networking
• How to Follow Up on a Cold Email
• Best Time to Send Cold Emails
How Does SMTP Send Mail?
Here's how it works step-by-step:
The Sender Writes an Email: Open your email client (like Gmail or Outlook), type your message, and click "send."
The Mail Client Sends the Email: Your email client connects to an SMTP server and sends your email to the server using the "MAIL FROM" and "RCPT TO" commands.
The SMTP Server Takes Over: The SMTP server acts as the mail carrier for your email, delivering it securely to the recipient’s server. It checks the recipient's domain (e.g., yahoo.com) to determine where to send it. If the recipient's domain matches the sender's, the email goes directly to the mail server.
Mail Transfer Agent (MTA) Finds the Recipient’s Server: If the email is for a different domain, the SMTP server connects to the recipient's mail server. The SMTP server uses DNS (Domain Name System) to locate the recipient's email server.
The Recipient’s Mail Server Receives the Email: The mail is delivered to the recipient's inbox. The mail delivery agent works with SMTP servers to securely deliver emails to the recipient’s inbox. This process includes filtering for spam or other security checks.
The Recipient Reads the Email: The email client (like Yahoo Mail or Outlook) retrieves the message and displays it for the recipient to read.
Types of SMTP Servers
Dedicated SMTP Server: Exclusively used by a single organization or user. Ensures high reliability and speed for email delivery. It is ideal for businesses with high email volumes.
Shared SMTP Server: Multiple users share the server resources. This is cost-effective for small businesses or low email volumes. However, due to shared usage, occasional delays may occur.
Cloud-Based SMTP Server: Hosted on cloud platforms for scalability. Offers high availability and easy integration with web applications. Examples: AWS SES, SendGrid, or Google Workspace.
ISP SMTP Server: Provided by Internet Service Providers to their customers, this server is simple for personal use but limited to business needs. It often comes with restrictions like email volume caps.
Transactional SMTP Server: Designed to handle automated, real-time messages (e.g., order confirmations, password resets). Ensures quick delivery and detailed analytics. Widely used in e-commerce and SaaS platforms.
Relay SMTP Server: This server acts as an intermediary, forwarding emails from one server to the recipient’s server. It is helpful for bypassing restrictions on local SMTP servers and is commonly used in hybrid systems. Relay servers are critical for email delivery across different mail servers and networks.
Internal SMTP Server: This server operates within an organization’s private network. It is secure, controlled, and suitable for sensitive communications. It requires in-house maintenance and expertise.
Open SMTP Server: This server accepts email delivery from any sender without authentication. It is rarely used today due to its vulnerability to spam and misuse. Although it was historically popular, it is now discouraged for security reasons.
Step-by-Step Guide to Setting Up an SMTP Server
Setting up an SMTP server might sound technical, but it's easier than you think. Follow these simple steps to get your email system running smoothly.
1. Choose Your SMTP Server
Decide whether you’ll use your ISP’s SMTP server, a cloud-based SMTP server, or set up your own. Popular options include:
Google Workspace
Email provider’s SMTP service
2. Install Necessary Software
For Windows: Use built-in features like the IIS SMTP server.
For Linux: Install software like Postfix or Sendmail.
Use commands such as:
`sudo apt-get update`
`sudo apt-get install postfix`
3. Configure the SMTP Server
Open your SMTP server settings.
Set the domain name (e.g., example.com) and outgoing mail server (smtp.example.com).
Configure the SMTP port (commonly 587 for TLS or 465 for SSL).
4. Set Up Authentication
Enable SMTP authentication to prevent unauthorized access.
Create a username and password for secure connections.
5. Test Your SMTP Server
Use command-line tools like Telnet or PowerShell for testing. For example: `telnet smtp.example.com 587` Send a test email to ensure everything works.
6. Enable Security Protocols
Configure TLS (Transport Layer Security) or SSL (Secure Sockets Layer) for encrypted communication. This ensures that your emails are safe during transit.
7. Integrate with Email Clients
Add your SMTP server details to your email client (like Outlook, Gmail, or Thunderbird).
Use settings such as:
SMTP Server: smtp.example.com
Port: 587 (TLS) or 465 (SSL)
Username: Your email address
Password: The password you created
8. Monitor and Troubleshoot
Check email logs regularly to identify issues. Use tools like delivery status notifications (DSNs) to track email performance.
SMTP Commands You Need to Know
1. HELO/EHLO
Used to introduce the client to the SMTP server. HELO is the older version; EHLO is its extended version, enabling modern SMTP features.
Example: EHLO mail.example.com
2. MAIL FROM
Specifies the sender’s email address. Begin the email transaction process.
Example: MAIL FROM:<sender@example.com>
3. RCPT TO
Identifies the recipient’s email address. It can be used multiple times to send emails to numerous recipients.
Example: RCPT TO:<recipient@example.com>
4. DATA
This signal tells the server the client is ready to send the email content. The email body follows this command, ending with a period on a new line (.).
Example: DATA Subject: Test Email This is a test email. Message contents, including text and attachments, are formatted and transmitted by the SMTP protocol.
5. QUIT
Terminates the SMTP session gracefully. Ensures that the server properly logs the session.
Example: QUIT
6. AUTH
Used for client authentication on the SMTP server. Supports different authentication methods like:
PLAIN
LOGIN
Example: AUTH LOGIN
7. STARTTLS
Initiates encryption for secure communication. Often used before sending sensitive email content.
Example: STARTTLS
8. RSET
Resets the current session without closing the connection. This is useful for correcting errors during email transmission.
Example: RSET. Other SMTP commands, like VRFY and NOOP, offer additional functionalities for debugging and testing.
9. VRFY
Verifies if a specific email address exists on the server. It is rarely used due to security and privacy concerns.
Example: VRFY user@example.com
10. NOOP
Sends a ping-like request to keep the connection alive without doing anything. Useful for maintaining long sessions.
Example: NOOP
Related Reading
• How Many Cold Emails Per Day
• Mailchimp for Cold Emails
• Best Bulk Email Sender
• Best Email Outreach Tools
• Bulk Email Providers
• Best Business Email Providers
• Best SMTP Server
• AI Tools for Email Marketing
• Amazon Ses Alternatives
• Postfix vs Sendmail
• Amazon Ses vs Sendgrid
Role of Mail Transfer Agent (MTA) in SMTP: Ensuring Efficient Email Routing
The Mail Transfer Agent (MTA) plays a crucial role in the Simple Mail Transfer Protocol (SMTP). It is the delivery driver for your emails, ensuring they reach the correct destination. A Mail Submission Agent (MSA) ensures that all outgoing mail relay messages are correctly formatted and delivered to the SMTP server. When you hit Send, the MTA transfers your message from the sender’s email client to the recipient’s mail server. Without the MTA, emails would have no way of navigating the complex paths of the internet to reach the intended inbox.
How the Mail Transfer Agent (MTA) Ensures Accurate and Efficient Email Routing
Here’s how the MTA works:
It receives the email from the SMTP server.
Then, it determines the recipient’s mail server using the Domain Name System (DNS), which matches the recipient’s domain to its mail server.
The MTA transfers the recipient's email addresses to the recipient's server for delivery.
This process ensures that emails are routed accurately and efficiently, even when they pass through multiple servers.
How to Set Up Gmail SMTP for Seamless Email Sending
1. Enable Gmail SMTP Access
Log into your Gmail account.
Go to Settings > See All Settings > Forwarding and POP/IMAP.
Enable IMAP Access and click Save Changes.
2. Generate an App Password
Visit your Google account's Security section.
If 2-step verification is not already enabled, turn it on.
Under "App Passwords," generate a unique password for SMTP access.
Use this password in the next steps.
3. SMTP Server Details
Use the following details for setup:
SMTP Server: smtp.gmail.com Port: 587 (for TLS) or 465 (for SSL)
Username: Your Gmail address (e.g., yourname@gmail.com)
Password: The App Password generated earlier.
4. Set Up in Email Clients or Application
Open your email client or application (e.g., Outlook, Thunderbird).
Add your Gmail account details.
Enter the SMTP server details from the previous step.
5. Test the Configuration
Send a test email to check if the setup works.
Double-check the port, server, and password settings if the email isn’t sent.
6. Troubleshooting Common Issues
Authentication Error: Ensure you're using the correct App Password.
Blocked Access: Check if Gmail flagged suspicious activity.
Firewall Issues: Confirm your network isn't blocking SMTP ports.
7. Advanced Configuration for Applications
For advanced integration, use tools like Postfix, PHPMailer, or Nodemailer.
Include your Gmail SMTP settings in the configuration file to automate email sending.
How to Address SMTP Error Codes
SMTP error codes are messages the mail server sends to explain why an email wasn’t delivered. They typically look like three-digit numbers (e.g., 550 or 421). Each number provides specific details about the issue.
Common SMTP Error Codes and What They Mean
550: Requested action not taken: The recipient's mail server rejected your email. It could be due to spam filters or a nonexistent email address.
421: Service not available: This occurs when the recipient’s server is temporarily unavailable.
451: Local error in processing: The sender’s email server encountered a temporary problem.
554: Transaction failed: The email was rejected because it was flagged as spam or contained errors.
How to Fix SMTP Errors
Check the Recipient’s Email Address: Ensure the email address is typed correctly. Even a small typo can cause errors like 550.
Review Your Email Content: If flagged as spam, remove suspicious links, large attachments, or repetitive keywords.
Retry Sending Later: Try again after some time for temporary errors like 421 or 451. Servers often resolve these issues quickly.
Update Your SMTP Settings: Confirm your SMTP server address, port, and authentication details are correct.
Contact the Server Administrator: If the error persists, contact the email provider or server admin for assistance.
How to Set Up an SMTP Server on Windows/Linux
Setting up an SMTP server on Windows or Linux systems and configuring one for web applications involves administrative rights and a basic understanding of your network and server environment.
Below, we'll go through the processes for both environments.
SMTP Server on Windows
For Windows Server (e.g., Windows Server 2019):
Install the SMTP Server Feature: Open the Server Manager. Go to "Manage" -> "Add Roles and Features". Navigate the wizard and select "SMTP Server" under the "Features" section.
Configure SMTP Service: After installation, open the Internet Information Services (IIS) 6.0 Manager (note: SMTP is managed through IIS 6.0 Manager even on newer servers). Right-click on "SMTP Virtual Server #1" -> "Properties". Configure general settings (e.g., IP address, port (usually port 25), and limits).
Set Up SMTP Email: Under "Access" tab, configure connection and relay restrictions. Under "Delivery" tab, configure outbound connections, advanced delivery options including smart host settings if you are relaying emails through an external SMTP server.
Secure Your SMTP Server: Restricting relay to prevent spam is crucial. Only allow your server IP or specific IP addresses to relay emails. Consider enabling TLS for secure email transmission.
Test Your SMTP Server: Use telnet or PowerShell (Send-MailMessage cmdlet) to send a test email and verify that your SMTP server works correctly.
SMTP Server on Linux
For Linux (e.g., using Postfix on Ubuntu):
Install Postfix: Run `sudo apt-get update` followed by `sudo apt-get install postfix`. During installation, you will be prompted to choose a configuration. For most users, "Internet Site" is appropriate.
Configure Postfix: Edit the main configuration file (/etc/postfix/main.cf) to set up domain, IP, and other settings. If applicable, specify myhostname, mydomain, myorigin, and relay host (relayhost).
Control Access and Relay: Edit /etc/postfix/main.cf to set up mynetworks (IP addresses allowed to send emails) and adjust relay controls.
Enable and Start Postfix: Run `sudo systemctl enable postfix` and `sudo systemctl start postfix` to enable and start Postfix automatically.
Test Your SMTP Server: Use commands like telnet or sendmail for basic email-sending tests to ensure the SMTP server is operational.
Send Emails with SMTP in Python
Python provides the smtplib library, which defines an SMTP client session object that can send mail to any Internet machine with an SMTP or ESMTP listener daemon. python
import smtplib
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
SMTP server configuration
smtp_server = "smtp.example.com"
port = 587 # For starttls
sender_email = "your-email@example.com"
password = "your-password"
receiver_email = "receiver@example.com"
Create the email message
message = MIMEMultipart("alternative")
message["Subject"] = "Test Email"
message["From"] = sender_email
message["To"] = receiver_email
Create the plain-text and HTML version of your message
text = """\
Hi,
This is a test email sent from Python."""
html = """\
<html>
<body>
<p>Hi,<br>
This is a <b>test email</b> sent from <i>Python</i>.
</p>
</body>
</html>
Attach parts into message container
part1 = MIMEText(text, "plain")
part2 = MIMEText(html, "html")
message.attach(part1)
message.attach(part2)
# Send the email
try:
server = smtplib.SMTP(smtp_server,port)
server.starttls() # Secure the connection
server.login(sender_email, password)
server.sendmail(sender_email, receiver_email, message.as_string())
finally:
server.quit()
Send Emails with SMTP in Java
The JavaMail API can send emails via SMTP. To use it, you need to include the JavaMail dependency in your project. java
import javax.mail.*;
import javax.mail.internet.*;
import java.util.Properties;
public class SendEmail {
public static void main(String[] args) {
String host = "smtp.example.com";
String user = "your-email@example.com";
String pass = "your-password";
String to = "receiver@example.com";
String subject = "Test Email";
String messageText = "This is a test email sent from Java.";
Properties props = System.getProperties();
props.put("mail.smtp.host", host);
props.put("mail.smtp.user", user);
props.put("mail.smtp.password", pass);
props.put("mail.smtp.port", "587");
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.starttls.enable", "true");
Session session = Session.getDefaultInstance(props, null);
MimeMessage message = new MimeMessage(session);
try {
message.setFrom(new InternetAddress(user));
message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
message.setSubject(subject);
message.setText(messageText);
Transport transport = session.getTransport("smtp");
transport.connect(host, user, pass);
transport.sendMessage(message, message.getAllRecipients());
transport.close();
} catch (MessagingException me) {
me.printStackTrace();
}
}
}
Send Emails with SMTP in Node.js
Node.js allows sending emails using SMTP with the help of the nodemailer module.
Install nodemailer using npm:
`npm install nodemailer`
Then, use the following code to send an email: javascript
const nodemailer = require('nodemailer');
let transporter = nodemailer.createTransport({
host: "smtp.example.com",
port: 587,
secure: false, // true for 465, false for other ports
auth: {
user: "your-email@example.com",
pass: "your-password",
},
});
let mailOptions = {
from: '"Sender Name" <your-email@example.com>',
to: "receiver@example.com",
subject: "Test Email",
text: "This is a test email sent from Node.js.",
html: "<b>This is a test email sent from Node.js.</b>",
};
transporter.sendMail(mailOptions, (error, info) => {
if (error) {
return console.log(error);
}
console.log('Message sent: %s', info.messageId);
});
How to Integrate SMTP with WordPress
Integrating SMTP (Simple Mail Transfer Protocol) with WordPress ensures that your website's emails are reliably sent through a professional mail server, significantly reducing the chances of your emails being marked as spam.
Here’s a step-by-step guide on how to set up SMTP in WordPress:
1. Choose an SMTP Plugin
WordPress does not natively support SMTP email configuration, so you must use a plugin. Several other SMTP email server plugins are available, but one of the most popular and user-friendly is "WP Mail SMTP" by WPForms.
How to:
Go to your WordPress dashboard.
Navigate to "Plugins" > "Add New".
Search for "WP Mail SMTP".
Click "Install Now" on the plugin, then activate it.
2. Configure the SMTP Plugin
After activating the plugin, configure it with your SMTP service providers' details.
How to:
In your WordPress dashboard, go to "WP Mail SMTP" > "Settings.”
The “From Email” and “From Name” options are here. The "From Email" should be the email address you want to send emails from, and it's recommended that this address be valid on your domain to improve deliverability.
Check the box that says “Set the return path to match the From Email" to ensure bounce messages are sent to the From Email address.
3. Choose Your SMTP Mailer
WP Mail SMTP allows you to choose from several free SMTP, email servers, and services, including:
Default SMTP
Sendinblue SMTP
Mailgun SMTP
SendGrid SMTP
Gmail SMTP (for Gmail or G Suite accounts)
Microsoft SMTP (Outlook.com and Office 365)
Amazon SES SMTP
Other SMTP
Select the mailer that best suits the same email domain and your needs. If you have an SMTP email server address, choose “Other SMTP.”
4. Enter Your SMTP Settings
If you selected "Other SMTP,” you must enter your own SMTP server name details.
These details typically include:
SMTP Host: The address of your SMTP server.
SMTP Port: Common ports include 587 (recommended for TLS encryption) and 465 (SSL encryption).
Encryption: Choose between SSL and TLS encryption. TLS is recommended if your SMTP server supports it.
Authentication: Enable authentication and enter the SMTP username and password provided by your SMTP service or hosting provider.
For other mailers, you will be prompted to enter API keys or OAuth credentials, which you can get from your email service provider's dashboard.
5. Test Your SMTP Settings
WP Mail SMTP provides an option to send a test email.
How to:
Navigate to "WP Mail SMTP" > "Email Test" in your WordPress dashboard.
Enter an email address where you want to receive the test email and click "Send Email.”
You should receive the test email confirming that your SMTP settings are correctly configured.
6. Save Your Settings
After successfully sending a test email, ensure all your settings are saved. Your WordPress site is configured to send emails using SMTP, improving email deliverability.
Start Buying Domains Now and Setup Your Email Infrastructure Today
Cold outreach is a tricky thing. You have to go through the spam folder to get a chance to connect with your prospects. Then, you must write an engaging email that compels your reader to act. The last thing you want to worry about in your cold outreach strategy is your email infrastructure. That’s why I recommend Inframails SMTP email infrastructure to all my clients. Inframail takes the headache out of cold emailing with unlimited Microsoft-backed inboxes for a single flat rate. The boost your cold outreach will get by using Inframails email infrastructure will make your emails more reliable and improve deliverability, so you can connect with more prospects and grow your business.
Simplifying Cold Outreach
Inframail allows scaling their outreach efforts efficiently without the technical headaches of traditional providers like:
Agencies
Recruiters
Sales development representatives (SDRs).
Features like automated SPF, DKIM, and DMARC setup will save you hours of technical setup time, while dedicated email servers for each user ensure you get the best performance for your cold outreach. With 16-hour priority support daily, you can even get help with your email infrastructure while you sleep.
How Inframail Empowers Agencies, Recruiters, and SDRs to Scale Outreach Without Technical Hassles
Forget traditional cold email providers that charge per inbox and leave you wrestling with technical configurations. Inframail streamlines the entire process. We handle the complex infrastructure setup while you focus on reaching more prospects.
InfraMail provides the robust email infrastructure you need without the usual technical headaches and per-inbox costs, whether you're:
An agency looking to scale outreach
A recruiter connecting with candidates
An SDR driving sales
Start buying domains now and set up your email infrastructure today with our email infrastructure tool.
Sending cold outreach emails can feel like a shot in the dark. You find the right prospects, craft the perfect message, and hit send, only to find that your email ended up in the depths of the spam folder—if it even got delivered. Implementing an SMTP Send Email strategy can help ensure your emails get delivered quickly and reliably by optimizing the sending process. In this blog, we'll explore the ins and outs of SMTP Send Email, revealing how it works and how cold emails tips can help you streamline your email-sending process for faster, more reliable communication.
One valuable tool for implementing an SMTP strategy is Inframail's email infrastructure. This solution helps optimize your email deliverability to boost your cold outreach success.
Table of Contents
What is SMTP (And What Does SMTP Stand For)?
What happens behind the scenes when you hit "Send" on an email? Enter SMTP—the Simple Mail Transfer Protocol. The silent workhorse ensures your messages travel across the vast expanse of the internet and land in the right inbox.
SMTP stands for Simple Mail Transfer Protocol—an application mail server that sends, receives, and relays outgoing emails between senders and receivers. SMTP is the protocol that allows you to send and receive emails. It is the technology behind email communication, and without it, email communication would be nonexistent since SMTP determines which servers will receive your relay messages.
The Simple Mail Transfer Protocol That Powers Email Communication
S = Simple: SMTP is designed to be straightforward to implement.
M = Mail: SMTP is built to send email messages across networks.
T = Transfer: SMTP transfers email messages from one server to another.
P = Protocol: SMTP is a set of rules (or protocols) that lets different email systems and servers communicate with each other.
SMTP is the digital postal service of the internet. It determines which servers will receive your messages and how they'll get there. Without SMTP, your emails would be like letters without addresses—they'd have nowhere to go.
What Does SMTP Do (and Not Do)?
As the “T” in its name indicates, SMTP is a transport protocol: It moves messages from point A to point B. Like many other Internet protocols, SMTP is intended to be used with the Transmission Control Protocol (TCP), which guarantees reliable delivery of the individual packets that make up a conversation.
Role and Limitations: Deliverability, Tracking, and Beyond
Using IP means that we can depend on SMTP to send the message contents to a server eventually, but what happens to it after that is up to the server? Imagine what happens when a delivery driver leaves a package at your office on a Saturday. What happens to it after delivery isn’t his problem.
Examples of services that SMTP doesn’t necessarily provide but are still very valuable are:
Deliverability
Monitoring
Tracking
Authentication
Encryption
What is an Email Server—and What Is an SMTP Server?
An outgoing mail server is a generalized term to describe a system that collects, processes, and serves email. Much like a mail carrier, every email message passes through the mail server before reaching its destination. Without servers, you could only send emails to people whose addresses matched your domain—Gmail.com to Gmail.com, for instance.
Because an SMTP email server pertains to outgoing email, it’ll have an address (or addresses) that the mail client or application you use can set that generally looks like this: smtp.serveraddress.com. For example, the SMTP server Gmail uses is smtp.gmail.com, and Twilio SendGrid’s is smtp.sendgrid.com. You can usually find your SMTP email server address in your mail client’s account or settings section.
How SMTP’s Store and Forward Process Ensures Reliable Email Delivery Across Networks
Using a store and forward process, SMTP works with the mail transfer agent to move your email across networks to the correct computer and email inbox. So when you send an email with SMTP host Gmail or AOL, the SMTP server processes your email, decides which server to send the message to, and relays the message to that email server. The recipient’s inbox service provider, such as Gmail or AOL, then downloads the message and places it in the recipient’s inbox. Our docs page provides more details to help you understand the meaning of SMTP.
What is an SMTP Email Service?
SMTP email services handle all the SMTP protocol details for you. They're email service providers (like Twilio SendGrid) that do all the behind-the-scenes work to get your emails adequately formatted, sent, and delivered to the recipient's mail server.
An SMTP email service manages your complex infrastructure. It does everything from:
Improving email deliverability
Securing sent emails
Providing valuable email performance analytics
Common SMTP server providers and settings
SMTP: Provider URL SMTP Settings
AOL: aol.com smtp.aol.com
AT&T: att.net smtp.mail.att.net
Comcast: comcast.net smtp.comcast.net
iCloud: icloud.com/mail smtp.mail.me.com
Gmail: gmail.com smtp.gmail.com
Outlook: outlook.com smtp-mail.outlook.com
Yahoo!: mail.yahoo.com smtp.mail.yahoo.com
How They Differ from Standard Servers
Is an SMTP server the same as a standard server? Like most servers, the SMTP server processes data sent to another server, but it has the specific purpose of processing data related to the sending and relaying of emails. An SMTP server is not necessarily on a machine but can be an application constantly running in anticipation of sending new mail.
Why are SMTP Servers Important?
When communicating over email, it's crucial to send email to your recipient safely and on time. Your email can’t reach its destination without an SMTP server. Once you hit Send, the email transforms into a string of code sent to the SMTP server, which processes that code to pass the message. Without the SMTP server to process the message, the message wouldn’t translate.
How SMTP Servers Verify Accounts and Handle Undeliverable Emails
The SMTP server verifies that the outgoing email is from an active account. In other words, the email server checks whether an active or working email account sent the outgoing message, protecting your inbox from illegitimate emails. If the email is undeliverable, the SMTP ensures the email will bounce back to the sender, letting them know they have an incorrect email address or the receiving email server blocked the email for whatever reason.
Related Reading
• How to Send Bulk Emails
• Outreach Automation
• How to Know if Someone Opened Your Email
• How to Send a Cold Email for Networking
• How to Follow Up on a Cold Email
• Best Time to Send Cold Emails
How Does SMTP Send Mail?
Here's how it works step-by-step:
The Sender Writes an Email: Open your email client (like Gmail or Outlook), type your message, and click "send."
The Mail Client Sends the Email: Your email client connects to an SMTP server and sends your email to the server using the "MAIL FROM" and "RCPT TO" commands.
The SMTP Server Takes Over: The SMTP server acts as the mail carrier for your email, delivering it securely to the recipient’s server. It checks the recipient's domain (e.g., yahoo.com) to determine where to send it. If the recipient's domain matches the sender's, the email goes directly to the mail server.
Mail Transfer Agent (MTA) Finds the Recipient’s Server: If the email is for a different domain, the SMTP server connects to the recipient's mail server. The SMTP server uses DNS (Domain Name System) to locate the recipient's email server.
The Recipient’s Mail Server Receives the Email: The mail is delivered to the recipient's inbox. The mail delivery agent works with SMTP servers to securely deliver emails to the recipient’s inbox. This process includes filtering for spam or other security checks.
The Recipient Reads the Email: The email client (like Yahoo Mail or Outlook) retrieves the message and displays it for the recipient to read.
Types of SMTP Servers
Dedicated SMTP Server: Exclusively used by a single organization or user. Ensures high reliability and speed for email delivery. It is ideal for businesses with high email volumes.
Shared SMTP Server: Multiple users share the server resources. This is cost-effective for small businesses or low email volumes. However, due to shared usage, occasional delays may occur.
Cloud-Based SMTP Server: Hosted on cloud platforms for scalability. Offers high availability and easy integration with web applications. Examples: AWS SES, SendGrid, or Google Workspace.
ISP SMTP Server: Provided by Internet Service Providers to their customers, this server is simple for personal use but limited to business needs. It often comes with restrictions like email volume caps.
Transactional SMTP Server: Designed to handle automated, real-time messages (e.g., order confirmations, password resets). Ensures quick delivery and detailed analytics. Widely used in e-commerce and SaaS platforms.
Relay SMTP Server: This server acts as an intermediary, forwarding emails from one server to the recipient’s server. It is helpful for bypassing restrictions on local SMTP servers and is commonly used in hybrid systems. Relay servers are critical for email delivery across different mail servers and networks.
Internal SMTP Server: This server operates within an organization’s private network. It is secure, controlled, and suitable for sensitive communications. It requires in-house maintenance and expertise.
Open SMTP Server: This server accepts email delivery from any sender without authentication. It is rarely used today due to its vulnerability to spam and misuse. Although it was historically popular, it is now discouraged for security reasons.
Step-by-Step Guide to Setting Up an SMTP Server
Setting up an SMTP server might sound technical, but it's easier than you think. Follow these simple steps to get your email system running smoothly.
1. Choose Your SMTP Server
Decide whether you’ll use your ISP’s SMTP server, a cloud-based SMTP server, or set up your own. Popular options include:
Google Workspace
Email provider’s SMTP service
2. Install Necessary Software
For Windows: Use built-in features like the IIS SMTP server.
For Linux: Install software like Postfix or Sendmail.
Use commands such as:
`sudo apt-get update`
`sudo apt-get install postfix`
3. Configure the SMTP Server
Open your SMTP server settings.
Set the domain name (e.g., example.com) and outgoing mail server (smtp.example.com).
Configure the SMTP port (commonly 587 for TLS or 465 for SSL).
4. Set Up Authentication
Enable SMTP authentication to prevent unauthorized access.
Create a username and password for secure connections.
5. Test Your SMTP Server
Use command-line tools like Telnet or PowerShell for testing. For example: `telnet smtp.example.com 587` Send a test email to ensure everything works.
6. Enable Security Protocols
Configure TLS (Transport Layer Security) or SSL (Secure Sockets Layer) for encrypted communication. This ensures that your emails are safe during transit.
7. Integrate with Email Clients
Add your SMTP server details to your email client (like Outlook, Gmail, or Thunderbird).
Use settings such as:
SMTP Server: smtp.example.com
Port: 587 (TLS) or 465 (SSL)
Username: Your email address
Password: The password you created
8. Monitor and Troubleshoot
Check email logs regularly to identify issues. Use tools like delivery status notifications (DSNs) to track email performance.
SMTP Commands You Need to Know
1. HELO/EHLO
Used to introduce the client to the SMTP server. HELO is the older version; EHLO is its extended version, enabling modern SMTP features.
Example: EHLO mail.example.com
2. MAIL FROM
Specifies the sender’s email address. Begin the email transaction process.
Example: MAIL FROM:<sender@example.com>
3. RCPT TO
Identifies the recipient’s email address. It can be used multiple times to send emails to numerous recipients.
Example: RCPT TO:<recipient@example.com>
4. DATA
This signal tells the server the client is ready to send the email content. The email body follows this command, ending with a period on a new line (.).
Example: DATA Subject: Test Email This is a test email. Message contents, including text and attachments, are formatted and transmitted by the SMTP protocol.
5. QUIT
Terminates the SMTP session gracefully. Ensures that the server properly logs the session.
Example: QUIT
6. AUTH
Used for client authentication on the SMTP server. Supports different authentication methods like:
PLAIN
LOGIN
Example: AUTH LOGIN
7. STARTTLS
Initiates encryption for secure communication. Often used before sending sensitive email content.
Example: STARTTLS
8. RSET
Resets the current session without closing the connection. This is useful for correcting errors during email transmission.
Example: RSET. Other SMTP commands, like VRFY and NOOP, offer additional functionalities for debugging and testing.
9. VRFY
Verifies if a specific email address exists on the server. It is rarely used due to security and privacy concerns.
Example: VRFY user@example.com
10. NOOP
Sends a ping-like request to keep the connection alive without doing anything. Useful for maintaining long sessions.
Example: NOOP
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Role of Mail Transfer Agent (MTA) in SMTP: Ensuring Efficient Email Routing
The Mail Transfer Agent (MTA) plays a crucial role in the Simple Mail Transfer Protocol (SMTP). It is the delivery driver for your emails, ensuring they reach the correct destination. A Mail Submission Agent (MSA) ensures that all outgoing mail relay messages are correctly formatted and delivered to the SMTP server. When you hit Send, the MTA transfers your message from the sender’s email client to the recipient’s mail server. Without the MTA, emails would have no way of navigating the complex paths of the internet to reach the intended inbox.
How the Mail Transfer Agent (MTA) Ensures Accurate and Efficient Email Routing
Here’s how the MTA works:
It receives the email from the SMTP server.
Then, it determines the recipient’s mail server using the Domain Name System (DNS), which matches the recipient’s domain to its mail server.
The MTA transfers the recipient's email addresses to the recipient's server for delivery.
This process ensures that emails are routed accurately and efficiently, even when they pass through multiple servers.
How to Set Up Gmail SMTP for Seamless Email Sending
1. Enable Gmail SMTP Access
Log into your Gmail account.
Go to Settings > See All Settings > Forwarding and POP/IMAP.
Enable IMAP Access and click Save Changes.
2. Generate an App Password
Visit your Google account's Security section.
If 2-step verification is not already enabled, turn it on.
Under "App Passwords," generate a unique password for SMTP access.
Use this password in the next steps.
3. SMTP Server Details
Use the following details for setup:
SMTP Server: smtp.gmail.com Port: 587 (for TLS) or 465 (for SSL)
Username: Your Gmail address (e.g., yourname@gmail.com)
Password: The App Password generated earlier.
4. Set Up in Email Clients or Application
Open your email client or application (e.g., Outlook, Thunderbird).
Add your Gmail account details.
Enter the SMTP server details from the previous step.
5. Test the Configuration
Send a test email to check if the setup works.
Double-check the port, server, and password settings if the email isn’t sent.
6. Troubleshooting Common Issues
Authentication Error: Ensure you're using the correct App Password.
Blocked Access: Check if Gmail flagged suspicious activity.
Firewall Issues: Confirm your network isn't blocking SMTP ports.
7. Advanced Configuration for Applications
For advanced integration, use tools like Postfix, PHPMailer, or Nodemailer.
Include your Gmail SMTP settings in the configuration file to automate email sending.
How to Address SMTP Error Codes
SMTP error codes are messages the mail server sends to explain why an email wasn’t delivered. They typically look like three-digit numbers (e.g., 550 or 421). Each number provides specific details about the issue.
Common SMTP Error Codes and What They Mean
550: Requested action not taken: The recipient's mail server rejected your email. It could be due to spam filters or a nonexistent email address.
421: Service not available: This occurs when the recipient’s server is temporarily unavailable.
451: Local error in processing: The sender’s email server encountered a temporary problem.
554: Transaction failed: The email was rejected because it was flagged as spam or contained errors.
How to Fix SMTP Errors
Check the Recipient’s Email Address: Ensure the email address is typed correctly. Even a small typo can cause errors like 550.
Review Your Email Content: If flagged as spam, remove suspicious links, large attachments, or repetitive keywords.
Retry Sending Later: Try again after some time for temporary errors like 421 or 451. Servers often resolve these issues quickly.
Update Your SMTP Settings: Confirm your SMTP server address, port, and authentication details are correct.
Contact the Server Administrator: If the error persists, contact the email provider or server admin for assistance.
How to Set Up an SMTP Server on Windows/Linux
Setting up an SMTP server on Windows or Linux systems and configuring one for web applications involves administrative rights and a basic understanding of your network and server environment.
Below, we'll go through the processes for both environments.
SMTP Server on Windows
For Windows Server (e.g., Windows Server 2019):
Install the SMTP Server Feature: Open the Server Manager. Go to "Manage" -> "Add Roles and Features". Navigate the wizard and select "SMTP Server" under the "Features" section.
Configure SMTP Service: After installation, open the Internet Information Services (IIS) 6.0 Manager (note: SMTP is managed through IIS 6.0 Manager even on newer servers). Right-click on "SMTP Virtual Server #1" -> "Properties". Configure general settings (e.g., IP address, port (usually port 25), and limits).
Set Up SMTP Email: Under "Access" tab, configure connection and relay restrictions. Under "Delivery" tab, configure outbound connections, advanced delivery options including smart host settings if you are relaying emails through an external SMTP server.
Secure Your SMTP Server: Restricting relay to prevent spam is crucial. Only allow your server IP or specific IP addresses to relay emails. Consider enabling TLS for secure email transmission.
Test Your SMTP Server: Use telnet or PowerShell (Send-MailMessage cmdlet) to send a test email and verify that your SMTP server works correctly.
SMTP Server on Linux
For Linux (e.g., using Postfix on Ubuntu):
Install Postfix: Run `sudo apt-get update` followed by `sudo apt-get install postfix`. During installation, you will be prompted to choose a configuration. For most users, "Internet Site" is appropriate.
Configure Postfix: Edit the main configuration file (/etc/postfix/main.cf) to set up domain, IP, and other settings. If applicable, specify myhostname, mydomain, myorigin, and relay host (relayhost).
Control Access and Relay: Edit /etc/postfix/main.cf to set up mynetworks (IP addresses allowed to send emails) and adjust relay controls.
Enable and Start Postfix: Run `sudo systemctl enable postfix` and `sudo systemctl start postfix` to enable and start Postfix automatically.
Test Your SMTP Server: Use commands like telnet or sendmail for basic email-sending tests to ensure the SMTP server is operational.
Send Emails with SMTP in Python
Python provides the smtplib library, which defines an SMTP client session object that can send mail to any Internet machine with an SMTP or ESMTP listener daemon. python
import smtplib
from email.mime.text import MIMEText
from email.mime.multipart import MIMEMultipart
SMTP server configuration
smtp_server = "smtp.example.com"
port = 587 # For starttls
sender_email = "your-email@example.com"
password = "your-password"
receiver_email = "receiver@example.com"
Create the email message
message = MIMEMultipart("alternative")
message["Subject"] = "Test Email"
message["From"] = sender_email
message["To"] = receiver_email
Create the plain-text and HTML version of your message
text = """\
Hi,
This is a test email sent from Python."""
html = """\
<html>
<body>
<p>Hi,<br>
This is a <b>test email</b> sent from <i>Python</i>.
</p>
</body>
</html>
Attach parts into message container
part1 = MIMEText(text, "plain")
part2 = MIMEText(html, "html")
message.attach(part1)
message.attach(part2)
# Send the email
try:
server = smtplib.SMTP(smtp_server,port)
server.starttls() # Secure the connection
server.login(sender_email, password)
server.sendmail(sender_email, receiver_email, message.as_string())
finally:
server.quit()
Send Emails with SMTP in Java
The JavaMail API can send emails via SMTP. To use it, you need to include the JavaMail dependency in your project. java
import javax.mail.*;
import javax.mail.internet.*;
import java.util.Properties;
public class SendEmail {
public static void main(String[] args) {
String host = "smtp.example.com";
String user = "your-email@example.com";
String pass = "your-password";
String to = "receiver@example.com";
String subject = "Test Email";
String messageText = "This is a test email sent from Java.";
Properties props = System.getProperties();
props.put("mail.smtp.host", host);
props.put("mail.smtp.user", user);
props.put("mail.smtp.password", pass);
props.put("mail.smtp.port", "587");
props.put("mail.smtp.auth", "true");
props.put("mail.smtp.starttls.enable", "true");
Session session = Session.getDefaultInstance(props, null);
MimeMessage message = new MimeMessage(session);
try {
message.setFrom(new InternetAddress(user));
message.addRecipient(Message.RecipientType.TO, new InternetAddress(to));
message.setSubject(subject);
message.setText(messageText);
Transport transport = session.getTransport("smtp");
transport.connect(host, user, pass);
transport.sendMessage(message, message.getAllRecipients());
transport.close();
} catch (MessagingException me) {
me.printStackTrace();
}
}
}
Send Emails with SMTP in Node.js
Node.js allows sending emails using SMTP with the help of the nodemailer module.
Install nodemailer using npm:
`npm install nodemailer`
Then, use the following code to send an email: javascript
const nodemailer = require('nodemailer');
let transporter = nodemailer.createTransport({
host: "smtp.example.com",
port: 587,
secure: false, // true for 465, false for other ports
auth: {
user: "your-email@example.com",
pass: "your-password",
},
});
let mailOptions = {
from: '"Sender Name" <your-email@example.com>',
to: "receiver@example.com",
subject: "Test Email",
text: "This is a test email sent from Node.js.",
html: "<b>This is a test email sent from Node.js.</b>",
};
transporter.sendMail(mailOptions, (error, info) => {
if (error) {
return console.log(error);
}
console.log('Message sent: %s', info.messageId);
});
How to Integrate SMTP with WordPress
Integrating SMTP (Simple Mail Transfer Protocol) with WordPress ensures that your website's emails are reliably sent through a professional mail server, significantly reducing the chances of your emails being marked as spam.
Here’s a step-by-step guide on how to set up SMTP in WordPress:
1. Choose an SMTP Plugin
WordPress does not natively support SMTP email configuration, so you must use a plugin. Several other SMTP email server plugins are available, but one of the most popular and user-friendly is "WP Mail SMTP" by WPForms.
How to:
Go to your WordPress dashboard.
Navigate to "Plugins" > "Add New".
Search for "WP Mail SMTP".
Click "Install Now" on the plugin, then activate it.
2. Configure the SMTP Plugin
After activating the plugin, configure it with your SMTP service providers' details.
How to:
In your WordPress dashboard, go to "WP Mail SMTP" > "Settings.”
The “From Email” and “From Name” options are here. The "From Email" should be the email address you want to send emails from, and it's recommended that this address be valid on your domain to improve deliverability.
Check the box that says “Set the return path to match the From Email" to ensure bounce messages are sent to the From Email address.
3. Choose Your SMTP Mailer
WP Mail SMTP allows you to choose from several free SMTP, email servers, and services, including:
Default SMTP
Sendinblue SMTP
Mailgun SMTP
SendGrid SMTP
Gmail SMTP (for Gmail or G Suite accounts)
Microsoft SMTP (Outlook.com and Office 365)
Amazon SES SMTP
Other SMTP
Select the mailer that best suits the same email domain and your needs. If you have an SMTP email server address, choose “Other SMTP.”
4. Enter Your SMTP Settings
If you selected "Other SMTP,” you must enter your own SMTP server name details.
These details typically include:
SMTP Host: The address of your SMTP server.
SMTP Port: Common ports include 587 (recommended for TLS encryption) and 465 (SSL encryption).
Encryption: Choose between SSL and TLS encryption. TLS is recommended if your SMTP server supports it.
Authentication: Enable authentication and enter the SMTP username and password provided by your SMTP service or hosting provider.
For other mailers, you will be prompted to enter API keys or OAuth credentials, which you can get from your email service provider's dashboard.
5. Test Your SMTP Settings
WP Mail SMTP provides an option to send a test email.
How to:
Navigate to "WP Mail SMTP" > "Email Test" in your WordPress dashboard.
Enter an email address where you want to receive the test email and click "Send Email.”
You should receive the test email confirming that your SMTP settings are correctly configured.
6. Save Your Settings
After successfully sending a test email, ensure all your settings are saved. Your WordPress site is configured to send emails using SMTP, improving email deliverability.
Start Buying Domains Now and Setup Your Email Infrastructure Today
Cold outreach is a tricky thing. You have to go through the spam folder to get a chance to connect with your prospects. Then, you must write an engaging email that compels your reader to act. The last thing you want to worry about in your cold outreach strategy is your email infrastructure. That’s why I recommend Inframails SMTP email infrastructure to all my clients. Inframail takes the headache out of cold emailing with unlimited Microsoft-backed inboxes for a single flat rate. The boost your cold outreach will get by using Inframails email infrastructure will make your emails more reliable and improve deliverability, so you can connect with more prospects and grow your business.
Simplifying Cold Outreach
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Agencies
Recruiters
Sales development representatives (SDRs).
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How Inframail Empowers Agencies, Recruiters, and SDRs to Scale Outreach Without Technical Hassles
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An agency looking to scale outreach
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