One of the RBLs / anti-spam black list server our mail servers monitor, as do many other providers, SpamCop.net by Cisco Systems suffered a major outage today affecting mail routing for some of our clients.
The issue was caused by Cisco failing to renew a do main name the system relies on as reported at https://www.bleepingcomputer.com/news/security/spamcop-anti-spam-service-suffers-an-outage-after-its-domain-expired/. As a result the system returned a false positive for all emails checked against it an thuse preventing the sending of those checked messages.
We have temporarily resolved the issue at our end by removing the RBL which may result in a temporary and slight increase in spam messages. However, once Spamcop is fully back online we will change back to the original configuration.
Any queued messages will no be sending. Any already returned will have been notified to the sender so they know to send them again.
Sorry for any inconvenience but this was an issue with a 3rd party system beyond our control.
UPDATE: All systems are now back to normal
