Sender reputation

What it means

Providers attach reputation mostly to two identifiers: the sending IP address and the authenticated domain. Google's Postmaster Tools describes reputation as determined by the sending behaviour of a domain or IP address, and says mail from senders with a high reputation is more likely to reach Gmail's inbox than spam.

The inputs recur across provider guidance and M3AAWG's best practices: spam complaints, mail to addresses that do not exist, spam trap hits, authentication results, sudden changes in volume and whether recipients engage. M3AAWG adds that any domain in a message (Return-Path, From, DKIM signature, HELO, reverse DNS, Reply-To and links) may be used to judge the sender.

Each provider keeps its own view, so a sender can be trusted at one and filtered at another. Third-party scores such as Sender Score are estimates from their own data, not what a given provider sees.