What happens when an IP gets blocklisted?

When an IP lands on a blocklist, mail sent from that IP gets rejected or filtered by mailbox providers who reference that list. The impact varies: some blocklists cause universal rejection; others affect only specific providers or result in spam folder placement rather than outright blocks.

ESPs respond by investigating the cause, typically spam complaints, spamtrap hits, or compromised accounts. They submit delisting requests to the blocklist operator, which may require evidence of remediation. Some blocklists delist automatically after a cooling period; others require manual review.

During recovery, ESPs may shift traffic to clean IPs or throttle sending from the affected IP. For shared pools, they identify and remove the sender responsible. For dedicated IPs, the account holder bears responsibility for fixing the underlying issue.

A quarantined ship must prove it's seaworthy before leaving the harbor.