What is Sender Reputation?

Sender reputation is a score, or a bundle of signals, that mailbox providers like Gmail and Microsoft maintain about every sending domain and IP address. It reflects how trustworthy your mail appears based on the history of what you have sent and how recipients have reacted to it.

The inputs are numerous: bounce rates, spam-complaint rates, spam-trap hits, authentication results from SPF, DKIM, and DMARC, sending volume and consistency, and above all engagement — opens, replies, and whether people move your mail out of spam or delete it unread. Positive engagement lifts reputation; complaints and bounces sink it.

Reputation exists at two levels. Domain reputation follows your sending domain everywhere and is increasingly the dominant factor, while IP reputation attaches to the specific address that delivers your mail. Shared IPs mean other senders' behavior affects you; dedicated IPs give you full control but require enough volume to sustain.

Because reputation is earned slowly and lost quickly, protecting it is a discipline: authenticate properly, verify lists to avoid bounces and traps, warm up new domains and IPs gradually, keep volume steady, and actively remove disengaged contacts. Once a domain is flagged as a poor sender, recovery can take weeks of careful behavior.