What does the mailscanner do to email attachments?

Attachments with suspicious file extensions (e.g. exe) will be renamed automatically: e.g., USELESS_EYE_CANDY.EXE would be renamed to USELESS_EYE_CANDY.DEFANGED12345-EXE, so that one cannot open the attachment thoughtlessly by double-clicking. The attachment first has to be saved to the hard disk and to be renamed to USELESS_EYE_CANDY.EXE before it can be opened.

Note: The mailscanner feature is not the same as the antivirus.