First, our belief is that this problem only affects a subset of Exchange servers. So far, we’ve only been able to see this on Exchange 2007, though it may affect others. The fix below is specific to Exchange 2007 only. Based on the evidence, it appears that an update from Microsoft on Tuesday night may have overridden a port setting for Exchange 2007; that is, it may have reset the port back to default.
Now, how to test and fix? (Again, this is for Exchange 2007 only.) You will have to do all of this at the commandline on the Exchange Server. First, check your current setting by typing in:
Get-SendConnector | fl
If the response is not port 587, then type the following command to fix:
Get-SendConnector | Set-SendConnector -Port 587