Sender reputation is the score mailbox providers assign you based on past behaviour. It lives at the domain level and the IP level, and it is the single biggest factor in whether you reach the inbox. Strong reputation buys you the benefit of the doubt; weak reputation gets you filtered before content is even read.
Domain reputation vs IP reputation
Domain reputation is tied to the sending domain in your From header. It is portable: if you switch ESPs or IPs, the domain reputation goes with you. IP reputation is tied to the specific IP address used to send. For most senders today, domain reputation is the bigger lever.
The signals that move it
- Engagement: opens, clicks, replies, archive vs delete.
- Complaints: people marking your mail as spam.
- Bounces: hard bounces in particular signal poor list hygiene.
- Spam-trap hits: a near-certain sign of stale or purchased data.
- Volume consistency: sudden spikes look suspicious.
- Authentication results: persistent SPF or DKIM failures erode trust.
How to protect it
The short version: send wanted mail to engaged people, consistently, from a properly authenticated domain. The longer version: verify your list, suppress aggressively, include one-click unsubscribe, keep cadence steady and watch the signals above on every send.
Check Google Postmaster Tools and Microsoft SNDS weekly. Both give you a direct readout of what those providers think of your domain and IPs.
How to recover when it slips
Cut volume hard, often to 10 to 20% of normal. Send only to your most engaged contacts. Fix whatever caused the slip (usually a list import or a deliverability shortcut). Hold for two to four weeks of clean signals, then ramp back gradually. There is no shortcut.
Frequently asked questions
How can I check my domain reputation?
Google Postmaster Tools shows Gmail's view of your domain and IPs. Microsoft SNDS does the same for Outlook. Both are free and worth checking weekly.
Does sender reputation reset if I change ESPs?
Domain reputation moves with you. IP reputation does not, so a fresh ESP usually means a fresh shared IP pool and a brief settling period.
Can a single bad send damage reputation?
Yes, particularly if it hits a spam trap or produces a complaint spike. Recovery from one bad send typically takes two to four weeks of clean activity.