All,
I had a problem where application servers that were relaying SMTP through the Exchange server were failing. It turned out to be that the person who had configured the receive connectors had entered them like 10.10.10.10-255.255.255.255. The intent was to specify one specific IP address by using a /32 subnet mask, but really was allowing the entire range. But it worked properly for 7 months before it started to fail. The problem is resolved, adding specific IP addresses instead of a range got it working properly. But why would that configuration be a problem? That is, what, ultimately, caused it to stop working?
Much thanks for any pertinent information!