Why your cold emails go to spam, and how to fix each cause

When a cold email lands in spam, people usually start by rewriting the copy and hunting for "spam words". That's almost never the cause. Work through this list in order, because each step is cheaper to check than the one after it.

Why cold email starts at a disadvantage

Nobody asked for your email, and spam filters exist to catch mail people didn't ask for. So there's no trick that makes unwanted email look wanted. What moves you to the inbox is sending to people who have a reason to care, in small enough numbers that they treat it like a normal message, and answer it.

First, make sure you actually have a problem

One test email landing in your own spam folder proves little. Run a placement test across several real mailboxes and providers, and look for a pattern. Fixing a problem you only imagine can do real damage.

1. Broken authentication

SPF, DKIM and DMARC prove the email really came from you. If one is missing or broken, you've lost before anyone reads a word. Google requires SPF or DKIM from every sender, and for anyone sending more than 5,000 messages a day to Gmail accounts, all three.

Fix: run your domain through the domain health checker.

2. Too much volume

Hundreds of cold emails a day from one mailbox will catch up with you. Sudden jumps are just as bad as high numbers.

Fix: around 30 campaign emails a day per mailbox, three mailboxes a domain, and more mailboxes when you need more. Here's the reasoning.

3. A new domain or mailbox with no warm-up

A brand-new mailbox has no history, and sending straight to strangers gives it a bad one.

Fix: about 14 days of warm-up first, then raise campaign volume slowly. How warm-up works.

4. A bad list

Bad lists are one of the failures I've seen again and again in six-plus years. Dead addresses bounce, and people who were never a fit press "report spam".

Fix: verify right before sending, keep bounces under 2%, and narrow your targeting.

5. Too many spam complaints

This is the signal filters trust the most. Gmail's line is 0.3%, and you want to stay under 0.1%.

Low engagement counts too: an email that nobody replies to, sent to thousands, tells filters that people don't want it.

Fix: make opting out easy, stop sending as soon as someone says no, and send only to people with a real reason to care.

6. A blacklisted domain or sending address

Fix: check the blacklist checker. If you're listed, pause that domain and find the cause before asking for removal.

7. The content, last of all

Content does matter a little. Attachments, lots of links, big images and shouty formatting don't help, and neither does a link to a domain with a bad reputation.

Fix: plain text style, no attachments, one link at most in the first email.

Already in spam? Do this

1. Pause campaigns on the affected domain. Leave warm-up running.
2. Fix whatever you found above.
3. Give it a couple of weeks, then restart at a low volume and retest.

If it's serious, follow the steps in rescuing a domain in spam. Sometimes the cheaper answer is to retire the domain, which is why cold email should never go out from your main domain.

mailzy watches each mailbox's health, rests the ones at risk, and has a placement test you can run before launch. See deliverability.