CLI tool to attach a txt file to an existing e-mail

From KMail I want to pipe e-mails through a script that uses antivir to scan the e-mail (now a tem file in disk) for virusses. If a virus is found I'ld like to include the result of the scan in the mail, either as a text in the mail body or as a "virusfound.txt" attachment. I had a look at some tools but I didn't find what I was looking for. Any suggestions anyone?