Cold Emailing
Feb 18, 2026
CEO and co-founder
Cold Email Service Provider Deliverability: How to Evaluate & Validate Claims
Updated February 9, 2026
TL;DR: Every vendor claims "best-in-class deliverability," but the technical reality depends on dedicated vs shared IPs. Shared pools expose you to bad actors who can burn the entire IP range. To validate claims: confirm dedicated IP disclosure, run Mail-Tester benchmarks targeting 9+/10, and pilot domains over 30+ days. Google Workspace costs $420/month for 50 inboxes. Flat-rate providers like Inframail charge $129/month for unlimited inboxes on dedicated IPs, saving $291/month plus hours of manual DNS setup.
At 9:17AM on Monday, your phone explodes with client Slack messages. Eight campaigns that hit 78% inbox rates last week just crashed to 51%. You check Mail-Tester. Your score dropped from 9.2 to 6.8 overnight. The cause? Someone else on your shared IP pool sent spam over the weekend, and now your 50 domains inherit the damage.
This is the deliverability nightmare that vague vendor promises cannot prevent. The problem is not that vendors lie. The problem is that "deliverability" means different things depending on the infrastructure underneath. A dedicated IP isolates your sending reputation so your behavior alone determines ESP trust. A shared IP pool ties your fate to every other sender on that range.
This guide gives you a practical framework to audit infrastructure providers before you migrate 50+ domains and discover the hard way that "high deliverability" came with asterisks.
Why vendor deliverability claims are often misleading
When your Google Workspace bill hits $847 for 100 inboxes and you start researching alternatives, every vendor's website looks identical: "high deliverability," "enterprise infrastructure," "guaranteed inbox placement." The marketing copy tells you nothing about the technical architecture underneath.
The "best-in-class" trap
When a provider claims "best-in-class deliverability" without disclosing technical specs, you're looking at a red flag. The question you need answered: are my emails sent from a dedicated IP that only I control, or from a shared pool where other senders affect my reputation?
We see IP reputation as the foundation of deliverability because Gmail and Outlook evaluate incoming messages based partly on the sending IP's history. If your IP has a clean record, you land in the inbox. If someone else on your shared pool sends spam, you inherit the damage.
The noisy neighbor problem destroys deliverability regularly. When one tenant on a shared IP engages in spammy behavior, receiving servers can blacklist the entire IP range.
Dedicated IPs vs. shared pools: The infrastructure reality
Think of shared IP pools 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.
The practical difference shows up in three ways:
Visibility: With dedicated IPs, you know exactly which IP sends your email. With shared pools, you often have zero visibility into who else uses the same infrastructure.
Control: Dedicated IPs let you build reputation methodically. Shared pools mean your reputation fluctuates based on factors you cannot control.
Accountability: When deliverability drops on a dedicated IP, you can diagnose and fix the issue. On shared infrastructure, you may never identify the root cause.
For a visual breakdown, watch this dedicated IP vs shared IP comparison that walks through the technical mechanics.
Step-by-step: How to validate cold email deliverability claims
Vendor claims are marketing. Your job is verification. Here's a three-phase framework to test whether a provider's infrastructure actually delivers.
Phase 1: The technical setup audit (SPF, DKIM, DMARC)
Before you can evaluate deliverability, your email authentication must be configured correctly. This means SPF, DKIM, and DMARC records need to be in place for every sending domain.
What each protocol does:
SPF (Sender Policy Framework): Specifies which IP addresses can send email on behalf of your domain.
DKIM (DomainKeys Identified Mail): Uses cryptographic signatures to verify email content hasn't been tampered with in transit.
DMARC: Tells receiving servers what to do when SPF or DKIM checks fail.
Manual configuration of these records across 50 domains is time-intensive. You're logging into Namecheap or GoDaddy, creating TXT records, waiting for DNS propagation, then testing each domain individually. That's time you could spend on sales calls or client strategy.
We auto-configure SPF, DKIM, DMARC, and MX records for every domain. No DNS panel access required.
"The setup is ridiculously fast. SPF, DKIM, DMARC, forwarding - all handled in literally seconds without me having to dig through docs or guess what records to add." - Verified user review of Inframail
Our SPF, DKIM, and DMARC setup tutorial shows the 2-minute configuration for 10+ inboxes.
Phase 2: The Mail-Tester benchmark (Targeting 9+/10)
Mail-Tester is the industry-standard tool for evaluating email configuration. It scores your email on a 0-10 scale based on authentication, content, and IP reputation.
Important clarification: A perfect Mail-Tester score indicates proper technical configuration, not guaranteed inbox placement. As MailReach explains, "you can have 10/10 on Mail-Tester and land totally in spam" because the tool scans your email against best practices rather than predicting actual inbox placement.
Score interpretation:
Score | Meaning | What to Do |
|---|---|---|
10/10 | Perfect technical configuration | Proceed with live testing |
9/10 | Strong configuration | Minor optimizations possible |
8-8.5/10 | Acceptable baseline | Investigate flagged issues |
Below 8/10 | Configuration problems | Fix before live campaigns |
The tool evaluates multiple factors through SpamAssassin analysis: authentication records, content quality, blacklist status, and HTML formatting.
When evaluating a new provider, send test emails from their infrastructure to Mail-Tester before running real campaigns. If you cannot achieve 9+/10 with clean test content, the infrastructure has fundamental issues.
Our deliverability testing shows 9.5/10 on Mail-Tester and 88% inbox rate via GMass.
Phase 3: Live volume testing and sample size requirements
Sending 10 test emails is not a deliverability test. You need meaningful volume over time to understand how infrastructure performs under real conditions.
Recommended testing parameters:
Duration: Run tests for at least 2-4 weeks to capture performance patterns
Volume: Aim for several thousand emails total across your test period
Measurement: Track inbox placement rate, spam rate, and bounce rate
Extended testing matters because deliverability often looks perfect initially, then degrades as volume increases or as ESP algorithms flag sending patterns.
This is why contract flexibility protects your pilot investment. You need month-to-month billing that lets you pilot domains for 30+ days without annual commitments. Forced quarterly or annual contracts before validation is a red flag.
Our guide on warming up inboxes after migration covers the proper ramp-up process.
Calculating the true cost of deliverability: A TCO framework
Platform fees are just the start. The full infrastructure stack determines whether you stay under the 2.5-3.0% infrastructure cost threshold that protects your margins.
Hidden costs: Warmup tools, domain rotation, and setup time
Domain registration: You need secondary domains for cold outreach (never send from your primary domain). Domain costs vary from $16.44 per year depending on the TLD. For 50 domains, budget $400-1,000 annually.
Email warmup: New inboxes need gradual volume increases to build sender reputation. Services like Warmup Inbox start at $15/month per inbox, while TrulyInbox offers unlimited warmup at $29/month.
Setup time: Manual DNS configuration across 50 domains consumes hours you could spend on sales calls or client strategy. Automated setup reclaims this time immediately.
Flat-rate vs. per-inbox pricing models
The pricing model determines how costs scale. Per-inbox pricing creates linear cost growth that can push infrastructure costs above 30% of client billings. Flat-rate pricing keeps infrastructure fixed regardless of inbox count.
TCO comparison for 50 inboxes:
Provider Type | Platform Fee | Per-Inbox Cost | Monthly Total |
|---|---|---|---|
Google Workspace | $0 | $420/month | |
Inframail (Unlimited) | $129 | $0 | $129/month |
Shared-pool competitor | $50-100 | $2-3 × 50 | $150-250/month |
For 200 inboxes, the gap widens dramatically and threatens your target 2.5-3.0% net margins:
Google Workspace: 200 × $8.40 = $1,680/month
Inframail: $129/month (unchanged)
That's $1,551/month in infrastructure savings. At $4,000 average client MRR, Google Workspace infrastructure alone consumes 42% of billings for one high-volume client, destroying unit economics.
"So affordable that it will make your unit economics work, even for lower ticket b2b businesses like ours." - Verified user review of Inframail
For help sizing your infrastructure, our email sending capacity calculator walks through the math.
Red flags to watch for during vendor evaluation
Lack of IP disclosure
If a vendor won't confirm whether their infrastructure uses dedicated or shared IPs, assume it's shared. Ask directly: "Will my sending come from IPs used only by my account, or shared with other customers?" Evasive answers tell you nothing.
Forced long-term contracts
Vendors confident in their deliverability offer month-to-month billing. Annual or quarterly commitments before validation suggest the provider knows customers might churn once they see real performance.
"Unlimited" claims with hidden caps
True unlimited means no inbox caps, no throttling, no surprise overage charges. Read the terms of service carefully. Ask about specific limits: maximum inboxes, maximum daily sends, maximum domains.
No referenceable customers at scale
Legitimate providers can connect you with existing customers running similar operations. If a vendor cannot produce references at your scale, their customer base may be smaller than marketing suggests.
"Outstanding deliverability backed by personable, professional support. 1 on 1 with co-founder was extremely helpful to learning more about deliverability and proper infrastructure set up." - Verified user review of Inframail
How Inframail solves the validation and cost challenge
We built Inframail to solve three specific problems that destroy agency margins: per-inbox pricing that scales faster than revenue, manual DNS configuration that consumes hours weekly, and shared IP pools that let strangers burn your deliverability.
Automated DNS configuration and dedicated IP transparency Inframail has 38 5-star reviews on Trustpilot.
Every Inframail account gets dedicated US-based IPs: 1 IP on the Unlimited Plan ($129/month) or 3 IPs on the Agency Pack ($327/month). Your sending reputation is isolated from other users by design.
We auto-configure SPF, DKIM, DMARC, and MX records for every domain. No DNS panel access required.
Our deliverability monitoring dashboard tracks domain health and alerts you to potential issues. The "phantom redirects" feature hides domain redirects from ESPs to protect your sending domains.
Real-world performance
We have 2,000+ customers running cold email campaigns on our infrastructure. Our published benchmarks: 9.5/10 on Mail-Tester, 88% inbox rate via GMass testing.
"I can set-up inboxes in 5mins while saving money on Google Workspace subscriptions and benefit from great deliverability. All of my campaigns on Inframail are on a >10% reply rate, which is really good." - Verified user review of Inframail
"We spent months hunting for a reliable cold-emailing stack. After repeated failures with another provider, we trialled two options—Inframail and a competitor. We chose the competitor. A month later, we switched back to Inframail. Zero issues since." - Verified user review of Inframail
For detailed setup, watch our Inframail 3.5 demo or the complete infrastructure guide for 2025.
The framework in this guide applies to any provider, including us. Run your own Mail-Tester benchmarks. Pilot domains for 30 days. Track inbox placement rates across real campaigns.
We offer month-to-month billing specifically so you can validate before committing at scale. No quarterly lock-ins. No annual contracts required.
Sign up to Inframail and get started today.
Frequently asked questions
How long does DNS setup take with Inframail?
Under 180 seconds per domain compared to 15-20 minutes manually. Customer testimonials report setting up inboxes in minutes including full SPF, DKIM, and DMARC configuration.
What's the difference between 1 dedicated IP and 3 dedicated IPs?
The Unlimited Plan ($129/month) includes 1 dedicated US-based IP. The Agency Pack ($327/month) includes 3 dedicated IPs. Multiple IPs let you segment sending by client or campaign type for added reputation isolation.
Does Inframail include email warmup?
No. The platform does not include built-in warmup. You'll need external tools like Warmup Inbox ($15/month per inbox) or TrulyInbox ($29/month for unlimited). Our DFY Email Campaign Setup package ($299/month) includes warmup configuration.
What sending platforms integrate with Inframail?
We generate IMAP/SMTP credentials that export to CSV. You can import directly to Instantly, Smartlead, and similar platforms.
What's a good test duration for a new provider?
2-4 weeks of sending, targeting several thousand total emails. Track inbox placement rate, spam rate, and reply rate across the full test period.
Key terms glossary
SPF (Sender Policy Framework): A DNS record that specifies which IP addresses can send email on behalf of your domain.
DKIM (DomainKeys Identified Mail): A cryptographic signature added to email headers that verifies message integrity.
DMARC: A policy that tells receiving servers what to do when SPF or DKIM checks fail. Options include none, quarantine, or reject.
Dedicated IP: An IP address used exclusively by your account for sending email. Your reputation is isolated from other senders.
Shared IP pool: Multiple users send email from the same IP addresses. Your reputation is affected by other senders' behavior.
Mail-Tester score: A 0-10 rating of email technical configuration quality. Target 9+/10 for optimal setup.
