Cold Emailing
Feb 4, 2026
CEO and co-founder
Cold Email Infrastructure Glossary: SPF, DKIM, DMARC & Deliverability Terms
The agency founder's infrastructure challenge
Scaling an agency from 5 to 15 clients means managing 50-200 cold email domains. Each domain requires SPF, DKIM, and DMARC configuration. Each inbox adds to your monthly infrastructure bill. Google Workspace Business Starter costs $7-8.40 per user per month, meaning 50 inboxes run $350-420/month before you factor in domain costs or warmup tools.
The operational bottleneck is real. Manual DNS setup through Namecheap, GoDaddy, or Cloudflare means logging into separate panels, creating TXT records, waiting 24-48 hours for propagation, and testing with Mail-Tester before campaigns can launch. One agency founder captured this frustration perfectly:
"Adding all those records would have probably taken dozens of hours. Instead all records were added within 10 minutes." - Verified user review of Inframail
Understanding the vocabulary of infrastructure is the first step to solving these inefficiencies. Every term in this glossary connects directly to your P&L, either through time savings or cost reduction.
Core infrastructure components
Before diving into authentication protocols, you need to understand the physical and digital assets that power cold email. These components form the foundation of every campaign you send.
Dedicated IPs vs. shared IP pools
Dedicated IP: A unique IP address used exclusively by your organization for sending email. Your sending behavior alone determines your reputation with mailbox providers like Gmail and Outlook.
Shared IP pool: A group of IP addresses shared among multiple email senders. According to SendGrid's documentation on shared IP pools, when senders share an IP address, the deliverability of their emails may be impacted if another sender using the same IP address violates email marketing regulations or sends spam.
The Mailgun guide on dedicated IPs explains that getting a dedicated IP address provides your organization with exclusive ownership, giving you full control over the management of the email sender reputation and deliverability tied to that IP.
Think of it this way: Shared IP pools work like carpool lanes where you're affected by other drivers. One bad actor spamming gets the whole range flagged. Dedicated IPs work like private lanes where your behavior alone determines reputation.
We provide dedicated US-based IPs with every plan (1 IP on Unlimited Plan, 3 IPs on Agency Pack). For a deeper comparison, watch our video on dedicated IP vs shared IP pools for cold email.
Sending servers and SMTP
SMTP (Simple Mail Transfer Protocol): The internet standard for transmitting email. SMTP is the technology that allows mail servers to send, receive, and relay outgoing email between senders and receivers. Without it, email communication would be nonexistent.
IMAP (Internet Message Access Protocol): The protocol for retrieving emails from a server, allowing you to view and manage your inbox. While SMTP handles sending, IMAP handles receiving.
The sending server acts as your digital post office. When you hit "send," your SMTP server packages the message, checks authentication records, and routes it to the recipient's mail server. The receiving server then uses your SPF, DKIM, and DMARC records to verify legitimacy before deciding where to place the email.
For common sending issues and troubleshooting, our SMTP mail issue scenarios guide covers the most frequent problems agencies encounter.
Authentication protocols: The technical pillars of trust
The "Big Three" authentication records prevent spoofing, verify message integrity, and tell receiving servers how to handle failures. Getting these right is non-negotiable for inbox placement.
SPF (Sender Policy Framework)
Definition: Cloudflare's SPF documentation describes SPF as an email authentication method that ensures the sending mail server is authorized to originate mail from the email sender's domain.
What it does: An SPF record is a DNS TXT record containing a list of the IP addresses that are allowed to send email on behalf of your domain. When a receiving server gets your email, it checks whether the sending IP matches what's listed in your SPF record.
Why it matters for your agency: If someone spoofs your domain (sends email pretending to be you), SPF helps receiving servers reject those messages. Without a valid SPF record, your legitimate emails look suspicious.
Think of SPF as your domain's ID card. It tells receiving servers: "These IP addresses are authorized to send on my behalf. Anyone else is an imposter."
A typical SPF record looks like this:
DKIM (DomainKeys Identified Mail)
Definition: According to Cloudflare's DKIM guide, DKIM is an email authentication method that permits a person, role, or organization that owns the signing domain to claim responsibility for a message by associating the domain with the message.
What it does: DKIM uses digital signature schemes based on public key cryptography to authenticate where an email came from and verify it actually came from a server that sends emails from that domain. A pair of cryptographic keys are used: a private key for the sender to sign messages, and a public key for the receiver to verify signatures.
Why it matters for your agency: The receiver uses the public key to validate the signature and check it against the hash value for the mail message received. If the two values match, this cryptographically proves the mail was signed by the indicated domain and has not been tampered with in transit.
Think of DKIM as a wax seal on a letter. It proves the message came from you and wasn't altered during delivery.
DMARC (Domain-based Message Authentication, Reporting & Conformance)
Definition: DMARC.org explains that DMARC is an email authentication, policy, and reporting protocol. It builds on the widely deployed SPF and DKIM protocols, adding linkage to the author ("From:") domain name, published policies for recipient handling of authentication failures, and reporting from receivers to senders.
What it does: A DMARC policy allows a sender's domain to indicate that their email messages are protected by SPF and/or DKIM, and tells a receiver what to do if neither of those authentication methods passes. The three policy settings are:
p=none: Monitor only, take no action on failures
p=quarantine: Send failed messages to spam
p=reject: Block failed messages entirely
DMARC Alignment: As Cloudflare's DMARC documentation notes, DMARC operates by checking that the domain in the message's "From:" field is "aligned" with other authenticated domain names. If either SPF or DKIM alignment checks pass, then the DMARC alignment test passes.
Why it matters for your agency: Without DMARC, there's no instruction manual for receiving servers when authentication fails. Your legitimate emails might get through, but you have zero visibility into failures or spoofing attempts.
Manual configuration of these three records across 50 domains takes 12+ hours. Watch our walkthrough on SPF, DKIM, and DMARC setup in 2 minutes for 10+ inboxes to see automated configuration in action.
Deliverability and reputation terminology
These metrics determine whether your campaigns actually reach prospects or disappear into spam folders. Confusing them leads to misdiagnosis of campaign failures.
Inbox placement rate vs. delivery rate
This distinction is critical and often misunderstood:
Delivery rate: The percentage of emails that reach the recipient's mail server without bouncing. According to Mailjet's deliverability guide, the delivery rate divides emails delivered by emails sent. A "delivered" email simply means it didn't bounce.
Inbox placement rate: The percentage of delivered emails that land in the primary inbox (not spam or promotions). Mailgun's inbox placement guide clarifies that the inbox placement rate divides the number of emails that reach the inbox by the number of emails delivered.
Why the distinction matters:
Metric | What it measures | What it hides |
|---|---|---|
Delivery Rate | Emails accepted by receiving server | Spam folder placement |
Inbox Placement Rate | Emails reaching primary inbox | Nothing (true performance) |
You can have a 98% delivery rate and a 45% inbox placement rate. That means more than half your "delivered" emails are rotting in spam folders where prospects never see them.
Industry benchmarks show average inbox placement rates around 77-88% for legitimate senders. Below 60% signals a serious infrastructure or reputation problem. Our guide on identifying spam placement and healthy metrics covers the warning signs to watch for.
Email warmup and the "cold start" problem
Definition: Litmus's warmup guide describes email IP or domain warming as slowly sending emails from a new IP address or domain name and gradually increasing send volume over time.
Why it exists: Fresh domains and IPs have no sending history. Mailbox providers like Gmail and Outlook are suspicious of unknown senders. Mailgun's domain warmup guide explains that domain warming is the process of methodically adding email volume to a new domain over several days or weeks to establish a positive sending reputation.
Warmup timeline: Achieving maximum deliverability takes four to eight weeks, depending on targeted volume and engagement.
What warmup involves:
Sending low volumes (10-20 emails/day) initially
Gradually increasing over 2-4 weeks
Generating positive engagement signals (opens, replies)
Building trust with ISPs before campaign-scale sending
We provide the infrastructure; you connect it to a warmup tool like Warmbox, Lemwarm, or Instantly's warmup feature. Our warmup guide for Inframail inboxes walks through the process step-by-step, and our blog covers how to warm up email domains for cold campaigns.
"InfraMail makes it remarkably easy to purchase domains, configure them correctly, create inboxes, and initiate warm-up immediately." - Verified user review of Inframail
Infrastructure economics and scaling terms
Understanding the business side of infrastructure separates profitable agencies from those bleeding margin on per-seat costs.
Cost-per-inbox and TCO models
Cost-per-inbox: The monthly expense for each sending mailbox, including platform fees, domain costs, and warmup tools.
Total Cost of Ownership (TCO): The complete monthly infrastructure bill across all components. This includes:
Platform/provider fees
Domain registration (amortized monthly)
Warmup tool subscriptions
Sending platform costs
TCO comparison for 50 inboxes:
Cost Component | Google Workspace | Inframail |
|---|---|---|
Platform Fee | $350-420/month ($7-8.40 × 50) | $129/month (flat rate) |
Domain Cost | ~$62.50/month (50 domains × $15/year ÷ 12) | ~$34/month (included pricing) |
Warmup Tool | External required | External required |
Monthly Total | $412.50-482.50 | $163 |
Annual Savings | — | $2,994-3,834 |
At 200 inboxes, Google Workspace climbs to $1,400-1,680/month in platform fees alone. Inframail stays at $129/month.
"So affordable that it will make your unit economics work, even for lower ticket b2b businesses like ours" - Verified user review of Inframail
For detailed calculations based on your sending volume, use our email sending capacity calculator.
Domain rotation and burn rates
Domain rotation: The practice of distributing sending volume across multiple domains to avoid hitting sending limits and protect individual domain reputations. Agencies treat domains as consumable assets.
Burn rate: The frequency at which domains become unusable due to reputation damage, blacklisting, or ESP restrictions. Healthy operations see 5-10% monthly burn; poor infrastructure can hit 30%+.
Why rotation matters:
Gmail and Outlook limit sending per domain
Spreading volume protects against single-point failures
Damaged domains can be retired without campaign collapse
Domain calculation example:
To contact 10,000 leads per month:
10,000 leads ÷ 22 business days = ~455 emails/day
At 30-50 emails/domain/day safe limit
Required domains: 455 ÷ 30 = ~15 active sending domains
Our getting started guide covers domain setup and our custom domains guide explains best practices for selection and management.
Complete cold email infrastructure glossary
Here are 25 essential terms in alphabetical order for quick reference:
Blacklist: A real-time database maintained by organizations like Spamhaus that identifies IP addresses or domains suspected of sending spam. Being listed results in emails being blocked or sent to spam folders. We offer blacklist monitoring and auto-delisting requests.
Bounce (Hard): A permanent delivery failure because an email address is invalid, a domain doesn't exist, or your IP is being blocked.
Bounce (Soft): A temporary delivery failure where the email address may be valid, but the email is returned because of a full mailbox or a down server.
CNAME Record: A DNS record that points one domain to another, often used for DKIM selectors and domain verification.
Cold Start Problem: The challenge of building sender reputation from zero when launching new domains or IPs. Solved through warmup sequences.
Dedicated IP: A unique IP address used exclusively by your organization for email sending. Reputation is entirely controlled by your behavior.
Delivery Rate: The percentage of emails accepted by receiving servers (not bounced). Does not indicate inbox vs. spam placement.
DKIM: DomainKeys Identified Mail. A cryptographic authentication method proving email origin and message integrity.
DMARC: Domain-based Message Authentication, Reporting & Conformance. The policy layer that instructs receivers how to handle SPF/DKIM failures.
DNS Propagation: The time required for DNS changes to update across all servers on the internet. Can take up to 48 hours, though often faster.
Domain Rotation: Distributing sending volume across multiple domains to protect reputation and avoid per-domain limits.
ESP (Email Service Provider): A service providing email sending infrastructure. Can be marketing-focused (Mailchimp) or transactional/infrastructure (SendGrid, Postmark).
IMAP: Internet Message Access Protocol. Used for retrieving and managing emails in your inbox.
Inbox Placement Rate: The percentage of delivered emails that land in the primary inbox (excluding spam and promotions).
ISP (Internet Service Provider): In email context, refers to major mailbox providers like Gmail and Microsoft (Outlook) who set delivery rules.
MX Record: Mail Exchanger record in DNS that tells the internet where to send incoming email for your domain.
Phantom Redirects: A technique that hides domain redirects from email service providers, preventing tracking domain penalties. Our phantom redirects guide explains the difference from standard redirects.
Sender Reputation: A score assigned to your domain and IP based on sending history, engagement rates, spam complaints, and authentication compliance.
Shared IP Pool: A group of IP addresses used by multiple senders. Your reputation is affected by other users' behavior.
SMTP: Simple Mail Transfer Protocol. The standard for transmitting email between servers.
Spam Trap: An email address used by ISPs and blacklist operators to identify spammers. Two types exist: "Pristine" (never a real address) and "Recycled" (previously valid but repurposed).
SPF: Sender Policy Framework. A DNS record listing IP addresses authorized to send email for your domain.
Spintax: Syntax for creating email variations by randomly selecting from bracketed options. Example: {Hi|Hey|Hello} creates three possible greetings.
Throttle Limits: The maximum number of emails providers allow in a given period to prevent spam. Exceeding limits triggers delays or blocks.
TXT Record: A DNS record storing text-based information. Used for SPF and DMARC policies.
Warmup: The process of gradually increasing sending volume from a new domain or IP to establish positive reputation with mailbox providers.
For visual walkthroughs of these concepts, watch our Ultimate Cold Email Infrastructure Guide for 2025 or our tutorial on sending 1000+ cold emails per day.
"Inframail has been absolute gold in terms of delivering a great customer experience, and allowing me to spin up cold email infrastructure at scale for my clients as easily and fast as possible" - Verified user review of Inframail
Sign up to Inframail and get started today. We automate SPF, DKIM, and DMARC configuration so you can focus on campaigns instead of DNS panels.
Frequently asked questions
How many domains do I need for 10,000 leads per month?
Approximately 15 active sending domains. At 10,000 leads across 22 business days (455/day) and 30 emails per domain per day safe limit, you need 15 domains minimum. Add 20-30% buffer for rotation.
How long does DNS propagation take?
Up to 48 hours in worst cases, though changes often propagate within 1-4 hours depending on TTL settings and DNS caching.
What is a good inbox placement rate?
70-80% is good, 85%+ is excellent. Below 60% indicates a serious infrastructure or reputation problem requiring immediate investigation.
Does Inframail include email warmup?
The Unlimited and Agency Pack plans provide infrastructure only. You connect to external warmup tools like Warmbox, Lemwarm, or Instantly's warmup. The DFY Email Campaign Setup package ($3,497 one-time or $299/month) includes free email account warmup.
What's the difference between delivery rate and inbox placement rate?
Delivery rate measures emails accepted by servers (not bounced). Inbox placement rate measures emails reaching the primary inbox. You can have 98% delivery and 45% inbox placement if most delivered emails land in spam.
Key terms quick reference
Term | One-line definition |
|---|---|
SPF | DNS record listing IPs authorized to send email for your domain |
DKIM | Cryptographic signature proving email origin and integrity |
DMARC | Policy instructing receivers how to handle authentication failures |
Dedicated IP | IP address used exclusively by your organization |
Inbox Placement | Percentage of emails reaching primary inbox (not spam) |
Warmup | Gradual volume increase to build sender reputation |
TCO | Total monthly cost across platform, domains, and tools |
