Upgraded a server recently, found out a day later that my outbound mail was being rejected… from the local server. Looked at all of the configuration files and found that none of them have changed. What the heck is going on?
After some digging and minor hair-pulling I found that the software was now obeying a directive that was in the documentation from years ago. So, basically, the software is now behaving as designed, but it broke the system that was working (for years) with an “incorrect” configuration.
I wonder how many other sysadmins come across the same issue.