ESP matching matters more than you think

If your cold emails aren’t landing in the inbox, it might not be your subject line.

Or your copy.

Or your follow-ups.

Sometimes, the issue starts with something more fundamental: your sending domain and the infrastructure behind it - specifically, whether you’re matching your prospect’s Email Service Provider (ESP).

This is what we call ESP matching - and if you’re not doing it, you’re probably losing deliverability points you didn’t even know existed.

So let’s go over how to go about ESP Matching and building an infrastructure that can handle anything.

First, find out what ESPs you’re sending to

Before you can match ESPs, you need to know which ones your prospects are using. That’s where our free ESP Checker comes in. Drop in any business email address and it’ll instantly tell you whether that recipient is using Gmail, Outlook, or another major provider.

Why does that matter?

Because email platforms - especially Gmail and Microsoft 365 - are more likely to trust and deliver messages coming from their own ecosystem. That means if you’re emailing a Gmail address from a Gmail domain, you’re playing on home turf. If you’re sending from Outlook to Outlook? Same advantage.

But if you’re sending from a random mail server or mixing providers across your sending domains without strategy… your emails are walking into a spam trap blindfolded.

The ESP mismatch problem

Here’s a common mistake we see:

A sender sets up all their cold email infrastructure using Gmail mailboxes, assuming that’s a safe bet. But their prospect list? 70% Outlook users.

What happens? Emails get flagged, filtered, or silently dropped - even if the copy is clean and the reputation is solid. Why? Because Outlook treats incoming Gmail-originated cold emails differently than emails from its own Microsoft 365 network.

The same logic applies in reverse. Gmail inboxes are more suspicious of cold outreach from Microsoft domains.

The fix? Build a diverse infra stack

ESP matching isn’t a guessing game. You can create a cold email infrastructure that mimics your target market’s email landscape - and that’s exactly what we’ve made possible with the Forge family of tools.

Once you’ve checked which ESPs your ICP uses, here’s how to match them:

• Use Mailforge to set up mailboxes quickly, with a shared infrastructure set up and easy domain management.

• Go with Infraforge if you need advanced controls, multiple IPs, domain masking, or API access.

• Then add Primeforge to the stack for high-reputation Gmail or Microsoft accounts - already optimized for cold outreach and configured with U.S. IPs.

The result? A cold outreach system that blends in with your prospect’s inbox environment, increasing trust and deliverability.

Because deliverability isn’t just about warming up and writing well.

It’s about knowing who you’re emailing… and sending like one of them.