Sender reputation is the score a mailbox provider keeps on each sending domain and IP address, built from bounce rate, spam complaints, spam-trap hits, authentication results, sending volume patterns and recipient engagement. It decides whether mail is accepted, throttled or filed as spam. Reputation is scored per domain, which is why outbound teams spread sending across several domains, and it recovers slowly: a domain that crosses the 2% bounce or 0.3% complaint line can take weeks of clean sending to return.
Google Postmaster Tools reports domain and IP reputation in four bands with spam rate and authentication; Microsoft SNDS reports per IP. Neither explains the score. The inputs you can see are your own bounce and complaint rates per campaign, which is where management happens.
Bounces are the input a sender controls before the send. Complaints are controlled by targeting and frequency. Spam traps are avoided by never sending to old, unverified or bought addresses; the spam trap explainer describes the types.
A domain sending 2,000 a day drops to "low" in Postmaster after one campaign to a bought list. Bounce rate was 9%. The team verifies the base, removes 1,300 invalid rows, halves daily volume, and sends only to confirmed valid. Reputation returns to "high" after 19 days of clean sending.
Verify a list or a single address. 100 free checks a month, unknowns refunded.
Verify Leads - FreeAyoub built BounceZero's 5-stage validation pipeline, its dedicated BGP-announced IP infrastructure, and the Patroni HA PostgreSQL cluster behind every verification. Previously built high-volume email delivery infrastructure. Trained at 1337 Benguerir (École 42 network, 2019). Open-source: bgp_analyzer.