Warn everyone you know not to open an e-mail with "Mail Server Report" in the subject line. This is a virus and a very bad one.

This one checks out and is a bonafide real virus so hence the warning. Any email with "Mail Server Report" in the subject line is a new virus and should not be opened. It comes with an attachment in 'zip format'. Apparently there is a Zip file attached so be very leary of anything with a zip file on it. The message tells you that a worm was detected in an e-mail that you sent out and asks you to open and install the attachment to fix the Problem.

Only, it IS the problem!  DO NOT DO IT -- delete the e-mail. This is a real threat. You can check it out at snopes:

http://www.snopes.com/computer/virus/mailserver.asp