How often are models retrained?

You send a perfectly good email on Monday. By Friday, the same email lands in spam. You didn't change anything. What happened? The filter did.

Spam filtering models aren't static. They're constantly being updated, sometimes within hours, sometimes on a slower cycle. Understanding how often they retrain helps you understand why your deliverability can shift without any warning.

The short answer is that most major providers run multiple models at different speeds. There's no single update cycle. Think of it as layers.

The fastest layer updates in near real time. When a new phishing campaign hits and thousands of users start hitting "report spam" within the same hour, those signals feed directly into detection systems. Gmail and Outlook have both confirmed they use continuous learning for threat detection. A new attack pattern can be recognized and blocked within hours.

Still the slower layer retrains on daily or weekly cycles, using accumulated data to update the baseline classification models. These are more stable, less reactive. They're less likely to swing wildly based on a single noisy day of signals.

Then there's the personalized layer. Individual mailbox behavior also feeds into how a filter treats you specifically. If someone never opens your emails and deletes them immediately, that pattern builds up over time and starts to shape where your next email lands for that person. This kind of personalized filtering updates constantly, without a fixed retraining cycle at all.

What does this mean for you as a sender? It means the filter's opinion of you isn't fixed either. Good recent engagement can improve your standing relatively quickly. A spike in spam reports can hurt you within days. The system is always watching and always adjusting.

It also means that consistent behavior matters more than any single send. A sender who maintains steady engagement signals over weeks is more resilient than one who spikes and crashes. The slow-cycle models reward consistency because they're trained on patterns, not moments.

(One honest caveat: none of the major providers publish their exact retraining schedules. What we know comes from patents, research papers, and observable behavior. The exact mechanics are proprietary.)

If you're noticing unexplained shifts in your deliverability, our free Email Header Analyzer can help you see what's actually happening at the filter level. Or if something feels urgent, our SOS hotline is free to use.