Sender Reputation
A score inbox providers assign to your sending domain and IP based on engagement, complaints, and bounces.
Sender reputation is how mailbox providers judge whether mail from you is wanted. It is tracked for your sending domain and for the IP addresses your mail comes from, and each provider keeps its own private view. Gmail, Yahoo and Microsoft build it from spam complaints, bounces to invalid addresses, spam-trap hits, authentication results and how recipients interact with your messages. A damaged reputation sends mail to spam or gets it rejected, and it recovers only as your sending improves over time.
How to check your sender reputation
There is no single public score. Google Postmaster Tools shows Gmail-side data for a domain you verify, including the user-reported spam rate, once you send enough daily volume for data to appear. Microsoft SNDS covers IP addresses you control. On an email platform's shared IP pool, IP reputation is largely the provider's job, so your domain reputation is what you manage.
In your own platform, track complaints, hard bounces and unsubscribes per campaign. A sudden rise in any of them usually shows up before inbox placement falls.
Domain reputation vs IP reputation
IP reputation follows the server addresses your mail leaves from. Domain reputation follows the domain you authenticate with SPF, DKIM and DMARC. Most small senders share IPs with other customers of the same platform, so domain reputation is the part that tells you apart from them, and it moves with you when you change platforms.
Common sender reputation mistakes
Moving to a new domain to escape a damaged one: the new domain starts with no history, and the same habits damage it again. Blasting old addresses that have never engaged in a single send. Sending without SPF, DKIM and DMARC, which leaves providers nothing reliable to attach reputation to. Dismissing complaints because the rate looks small: Google's hard limit of 0.3% is about 3 complaints for every 1,000 messages.