One morning, email on our primary domain just... stopped working.
No bounce messages. No error a normal user would ever see. Outgoing mail vanished into nothing, and nothing was coming in either. For a small agency where half of new business arrives by email, that's not a minor inconvenience — that's the front door nailed shut.
Opening the Ticket
First instinct was to check the obvious stuff: DNS records, mail server config, SPF/DKIM — all fine. So we opened a support ticket with our hosting provider and waited.
The answer that came back wasn't what we expected: our server's IP address had landed on the Spamhaus blacklist — one of the most widely used spam-reputation lists in the world. Once an IP is on it, a huge percentage of mail servers worldwide will silently drop or reject anything coming from that address. That's why we weren't seeing bounces — recipient servers weren't even bothering to tell us.
