I have about 10 domains all filtered thru our spam filter, all going to DIFFERENT exchange servers. Something happend about 5pm yesterday that has cause 3 of the 10 to not receive mail any longer.
All have no windows firewall or other known firewall. No Antivirus / Malware software on them. Very clean boxes.
Nothing has changed honestly on these boxes in years. If you run telnet locally you get a flashing cursor not the typical header response. I've restarted the services, made sure relaying was set appropriately etc.....