In some cases sending an Email from WebClient can lead to a Bluescreen.
When sending an Email from WebClient the Click Once Application is executed.

To fix the behavior you have to delete the Click Once Cache:

rundll32 %windir%\system32\dfshim.dll CleanOnlineAppCache

Make sure you run this command as the user who gets the Bluescreen when sending an Email.
Install also this Microsoft Hotfix:
If this does not help, please try to delete the cache manually:
Windows Vista and higher: %userprofile%\AppData\Local\Apps\2.0\
Windows XP: %userprofile%\Local Settings\Apps\2.0\
Just delete the content of the 2.0 directory.
If there are the behavior persists the Bluescreen Dump has to be analyzed.