Blacklist
A database of IP addresses or domains known to send spam, used by email providers to block unwanted email.
Email blacklists (also called blocklists or DNSBLs) are maintained by organizations like Spamhaus, Barracuda, and SORBS. If your IP or domain ends up on a blacklist, your emails will be blocked or sent to spam by providers that use that list.
Common causes: high spam complaint rates, sending to spam traps, high bounce rates, sudden volume increases, and compromised accounts. You can check your status on major blacklists using MXToolbox or GlockApps.
Getting delisted typically requires: identifying and fixing the cause, submitting a delisting request to the blacklist operator, and waiting 24-48 hours. Prevention is better than cure — monitor your reputation proactively.