When in doubt, check your firewall and/or anti-virus settings

When using the System.Net.Mail.SmtpClient class in .NET, you may get a wonderful generic error that says the following:

The SMTP host was not found. --> Unable to connect to the remote server. --> An established connection was aborted by the software in your host machine.

I first read that as IIS was killing the connection and checked my permissions.  Everything was fine.  It turned out to be the McAfee Virus console that was blocking port 25.  Yet another good reminder that when having connection issues, check the firewall and anti-virus software settings!