Some potential issues have been identified with the current patched version of McAfee, which, among other things, can cause problems with sending mail via Thunderbird.
Here’s the Hotfix (Link at bottom)
Some discussion (McAfee Forum)
Author: Kevin
Manager of OIT Software Support
Screen shots, software updates and more:
http://osxdaily.com/2006/11/22/ten-os-x-command-line-utilities-you-might-not-know-about/