Definition
An ongoing score inbox providers assign to a sending domain or IP based on past behaviour, deciding whether future emails land in the inbox or get routed to spam.
It's built from signals like spam complaint rate, bounce rate, and how often recipients open or reply, and it's cumulative: one bad sending burst can suppress deliverability for weeks after, which is why reputation is monitored continuously rather than checked once.
Where this comes from
Read: Cold Email Deliverability: Why Your Emails Land in Spam (And How to Fix It)