How is reputation measured and scored internally by providers?
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You'll never get a printout from Gmail saying "your reputation score is 74." Mailbox providers keep their exact formulas private. But we know enough about what goes into the calculation to actually do something useful with that information.
The signals providers weigh most heavily are spam complaint rates, spam trap hits, engagement ratios (opens, clicks, deletes without opening), bounce rates, and whether your authentication passes cleanly every time. Machine learning models continuously adjust how much each signal matters based on new spam patterns. It's not a static formula. It shifts.
Gmail does expose a simplified version of its internal scoring through Postmaster Tools. Your domain reputation shows up as one of four categories: High, Medium, Low, or Bad. That's not the full picture of what Gmail tracks internally, but it's the clearest public window into how your domain is performing with Google's users.
Outlook (and Microsoft 365) offers something similar through SNDS (Smart Network Data Services), which uses traffic light indicators to show how your sending IPs are perceived. Green means you're fine. Red means you have a problem. Yellow means watch yourself.
What both tools are showing you is a simplified view of far more complex internal systems. Think of it like a credit score. You see the number. You don't see the model. But you can still influence the outcome by doing the right things consistently.
The score is dynamic. Every message you send, every complaint filed, every spam trap hit, every ignored email, it all feeds back into the calculation in near real time. A single bad campaign won't destroy years of good sending, but a pattern of bad behavior compounds quickly. Reputation also decays if you go quiet for too long, which catches a lot of senders off guard after a sending pause.
If you want to move from Low to High reputation in Postmaster Tools, the path is boring but it works. Lower your complaint rate below 0.1%, stop mailing unengaged subscribers, fix any authentication gaps, and send consistently rather than in bursts. You can check your authentication setup for free with our SPF checker or DKIM lookup if you want to rule that out first.
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