Is deliverability luck or logic?

You've probably heard someone say their emails "just ended up in spam" with a shrug, like it was the weather. But deliverability isn't luck. It's logic. And once you see the patterns, you can't unsee them.

Mailbox providers like Gmail and Outlook aren't rolling dice when they decide where your email lands. They're running calculations. Every message gets evaluated against a set of signals they've been refining for years.

The four main signals are things you actually control:

• Authentication. Does your sending domain have valid SPF, DKIM, and DMARC records? Without these, mailbox providers have no proof you are who you say you are.
• Reputation. What's your history? High complaint rates, lots of bounces, and sudden volume spikes all leave marks on your sender reputation.
• Engagement. Are your subscribers opening, clicking, and replying? Or are they ignoring and deleting? Mailbox providers treat low engagement as a quiet vote against you.
• Sending practices. Do you clean your list regularly? Do you send to people who actually opted in? Do you honor unsubscribes fast?

When deliverability looks random, it almost always means one of these signals is off. Authentication is broken, reputation has slipped, engagement has dropped, or a sending practice changed and nobody noticed. The variables aren't mysterious. They're just not yet visible.

Individual email outcomes can vary (complex filter interactions, domain-level quirks, inbox-specific rules), but the aggregate pattern is consistent. Good practices produce better results than poor ones, reliably and repeatedly.

That's the thing about logic: once you know the rules, you can run experiments, diagnose problems, and fix them. Luck doesn't give you that. Logic does.

If you want to start with a quick audit, check whether your SPF record and DMARC policy are set up correctly. Those two alone account for a surprising number of "random" deliverability problems. You can run both checks free at our SPF checker and DMARC parser.