How do spam filters evaluate ongoing sender behavior?

You send a campaign, it lands in the inbox. You send another one, and suddenly it's hitting spam. What changed? Probably nothing you did today. Spam filters don't just look at the email in front of them. They're constantly building a picture of who you are as a sender over time.

Here's what they're actually tracking on an ongoing basis.

Volume patterns. Filters notice how much mail you send and how consistently you send it. A sudden spike from 500 emails a week to 50,000 looks suspicious, even if every address is legitimate. Consistency matters as much as volume.

Complaint rates. When someone hits "This is spam", that signal goes back to the mailbox provider. Gmail and Outlook both use feedback loops to collect these signals. A complaint rate above 0.1% starts to hurt. Above 0.3% and you're in real trouble.

Bounce rates. High bounce rates tell filters your list quality is poor. Unknown users, inactive addresses, typos. Filters read that as a sign you're not managing your list carefully.

Engagement trends. Opens, clicks, replies, and deletes are all signals. If your subscribers consistently ignore your mail or delete it without reading, that pattern accumulates. Filters gradually lose confidence in your messages. If they engage, the opposite happens.

This evaluation happens at two levels at the same time. Your IP reputation and your domain reputation are tracked separately but weighted together. Switch IPs and your domain history travels with you. Build a clean IP reputation and a problematic domain will still drag you down. Neither one operates in a vacuum.

The question most senders actually want answered is this: how far back do filters look, and can past problems be fixed?

But most major mailbox providers weight recent behavior more heavily than old behavior. Gmail's systems, for example, are known to shift assessments within weeks when sending patterns improve noticeably. A rough patch from six months ago won't haunt you forever, but it also doesn't disappear overnight. Think of it as a rolling window where the last 30 to 90 days carry the most weight.

Recovery is real but it's gradual. Cleaning your list, cutting your sending frequency temporarily, and focusing on your most engaged subscribers are the fastest ways to rebuild. Don't try to fix a reputation problem by sending more. That makes it worse.

If you're not sure whether your current reputation is working for or against you, our free blocklist checker is a good first check. For a fuller picture, our SOS hotline is free and we'll walk you through what's actually happening.