I had problems with the e-mail function of CS 1.1. The cs_Exceptions table in the CS database had the following exception entry logged:

System.Runtime.InteropServices.COMException (0x80040211): The message could not be sent to the SMTP server. The transport error code was 0x800ccc15. The server response was not available.

According to Microsoft Support, 0x800ccc15 means:

0x800CCC15   SOCKET_CONNECT_ERROR           Unable to open Windows Socket.

So, the system couldn't set up a TCP socket to my SMTP relay box, which was confirmed by the output of a netstat -an | findstr ":25".

Then it hit me... I have Mcafee Virusscan 8 running on my server including the Access protection rules and guess what. Virusscan thought a mass worm/virus mailer was spamming my SMTP relay box and refused the socket connect attempt, made by the aspnet_wp.exe (IIS 6.0 worker process). See log entry:

<timestamp removed> Blocked by port blocking rule  aspnet_wp.exe Prevent mass mailing worms from sending mail a.b.c.d

Adjusting this rule proved to be the solution and this is confirmed by the log of my SMTP relay box.