Sender reputation
Sender reputation is the standing a mailbox provider assigns your sending domain and IP, based on how recipients have responded to your mail, and it decides whether future mail reaches the inbox.
Sender reputation is the running judgement each mailbox provider keeps about your sending domain and IP address. It is not one number and not published: Google, Microsoft and every other provider maintain their own, from their own users' behaviour, and none of them will tell you what it is. You infer it from outcomes.
What feeds it is recipient behaviour, weighted towards the negative. Complaints, marking as spam, and deleting without opening push it down. Bounces push it down hard, because mailing addresses that do not exist demonstrates a list you did not verify. Opens, replies, and being moved out of spam push it up, and replies count for more than opens because they are harder to fake. Volume itself is neutral; sudden changes in volume are not.
The asymmetry is what matters operationally. Reputation falls in days and recovers over weeks or months, and there is no way to appeal or reset it. This is why sending caps, verification before sending, and stopping automatically on a complaint spike are worth enforcing in code rather than leaving to judgement. By the time a person notices the problem in a dashboard, the damage is already done and the recovery is slow.
In practice
- A complaint rate crossing 0.3%, after which Gmail begins filtering most of a domain's mail.
- A domain that sent to a stale list once and spent two months recovering its inbox placement.
- A circuit breaker that stops sending automatically when bounces exceed a threshold, rather than waiting for someone to look.
Questions
How do I check my sender reputation?
You cannot read it directly, but you can read proxies. Google Postmaster Tools shows a domain reputation band and a spam rate for Gmail specifically, which is the closest thing to a direct reading. Beyond that, your own bounce rate, complaint rate and reply rate are the signals worth watching, plus whether inbox placement differs between providers. A drop that shows up at one provider and not others points at that provider's judgement rather than at your list.
How long does it take to repair a damaged reputation?
Weeks at best, months if the damage was severe, and only if the sending behaviour that caused it stops. Providers weight recent behaviour most heavily, so a period of low-volume, high-engagement sending is what rebuilds standing. There is no reset and no appeal. Moving to a new domain starts a fresh reputation but also starts from zero history, which means warming up again.
Does reputation follow the domain or the IP?
Both, tracked separately. On shared sending infrastructure the IP reputation is partly other senders' doing, which is an argument for a dedicated IP at volume and against one at low volume, where a dedicated IP simply has too little traffic to build a history. Domain reputation is yours alone and is the one that follows you between providers.
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