You've written a solid email. The subject line is direct. The copy is tight. You hit send on 50 prospects and... nothing. No opens. No replies. Just silence.

Odds are good your emails ended up in spam.

This is the most frustrating part of cold email - you can do everything right on the copy side and still fail because of infrastructure. Gmail's spam filters are ruthless, and they're only getting smarter. But here's what most people miss: spam filtering isn't random. It's predictable. And you can control most of it.

I'm going to walk you through the specific things that trigger spam filters and exactly how to fix them. Not vague tips. Real, measurable changes you can implement today.

Domain Reputation is Everything

Every email you send from a domain has a reputation score attached to it. Gmail, Outlook, and Yahoo all track this. If your reputation is bad, your emails get filtered. If it's good, they land in the inbox.

The problem: most people don't know their domain's reputation and don't check it until they're already in trouble.

Start here. Go to MXToolbox and run a reputation check on your sending domain. Look for your domain in any blacklists - if you're on a list, that's why your emails are getting filtered. You can also check Return Path's domain reputation tool.

If you're on a blacklist, you'll need to delist. Most lists have a form you fill out, but the real fix is making sure you don't get back on it. That means:

If your domain is clean but still having issues, the problem might be your sending volume or sending pattern. If you send 10 emails one day and 500 the next, email providers get suspicious. Ramp up gradually. Start with 20-30 emails a day and increase by 10-15% each day until you hit your target volume.

SPF, DKIM, and DMARC - These Actually Matter

These are the three things that tell email providers: "Yes, this person is authorized to send from this domain." If you don't have them set up, spam filters assume you're spoofing and dump your email in spam.

Here's what you need:

SPF (Sender Policy Framework): This is a DNS record that lists which IP addresses are allowed to send emails from your domain. It takes 15 minutes to set up. Go to your DNS provider (GoDaddy, Namecheap, etc.) and add an SPF record that includes your email provider. If you're using Gmail, it looks like this:

v=spf1 include:_spf.google.com ~all

DKIM (DomainKeys Identified Mail): This cryptographically signs your emails so providers know they haven't been tampered with. Most email providers will generate this for you automatically - you just need to add it to your DNS. Check your email provider's settings - there's almost always a DKIM setup section.

DMARC (Domain-based Message Authentication, Reporting and Conformance): This tells email providers what to do if an email fails SPF or DKIM checks. Add this DNS record:

v=DMARC1; p=quarantine; rua=mailto:[email protected]

This will quarantine suspicious emails and send you reports. After a week of monitoring reports, you can change "p=quarantine" to "p=reject" for stricter filtering.

These three things take about 30 minutes total to set up and will improve your deliverability by 15-30% immediately.

Warm Up Your Domain First

This is the mistake that kills most new campaigns: you register a domain, set up email, and immediately blast out 200 cold emails. Email providers see a new domain sending a large volume to unknown recipients and flag it as spam.

Instead, warm up your domain for 7-10 days before you start your real campaign. Here's the process:

The goal is to show email providers that your domain is legitimate before you scale. A 10-day warmup period will reduce spam filtering by 20-40%.

Write Copy That Doesn't Trigger Filters

Even with perfect infrastructure, certain words and patterns trigger spam filters. Here's what to avoid:

Here's an example of an email that passes spam filters and still converts:

Hey [Name], Quick thought - most [role] we talk to spend 20+ hours/month on [specific task]. We help [service business type] cut that down to 3-4 hours using [specific method]. Worth 15 min to explore? [First name]

This has no trigger words, no excessive formatting, and focuses on the recipient. It lands in the inbox and it converts.

Monitor Your Metrics

Don't wait until your entire campaign fails to check if emails are hitting spam. Monitor these metrics from day one:

Check these daily for the first two weeks. If something is off, you'll catch it early.

Related Guides

The gap between knowing this and executing it: Deliverability is technical, it's boring, and it requires monitoring. Most people either skip it entirely or set it up wrong and never come back to it. If you'd rather focus on the sales side - writing copy that converts, handling replies, closing deals - that's where a cold email agency makes sense. We handle the infrastructure, monitor deliverability continuously, and manage the entire campaign so your emails consistently land in the inbox. That's what frees you up to close clients.