non-stop incoming e-mail message

The message originated from another machine that was infected and sent out the email from that persons contacts list,check the sever to check the virus and start the process of deleting it.
Check the anti-virus software manufacturer's web site for ereadicating the virus,if the machine is on a network it is best to take the machine off the network connection.
Check the C:\Windows directory to see if the file exist and you will see how large it is

This is probably a similar problem that occurs with McAfee's AVD where the On Access Scan picks up the infected message from the incoming queue and quarantines it before the message has completed downloading. This will cause a download error with the Exchange IMC and the message will not be removed from the ISP's SMTP server and it will be delivered the next time that the IMC connects. The problem can be solved by excluding the queue folders from the on-access scanner. The folder location will depend on your individual setup of exchange but it will be called 'Drive:'\exchsrvr\imcdata\ and there will be sub-folders. You do not need to worry about not scanning these folders as this is the working area of the Mail Scanner.
To find the senderof the message open one of the quarantined files in Notepad (the payload will note run as this will be a MIME\UUEncoded text file) then you can read the headers of the message.

Hope this helps

Chris