scanning for filetype?

[ISP List]

>The 'file' command does a pretty good job. File::MMagic is a perl module
>to do the same thing... it could be done, but would slow things down.
>
>I don't know whether there's a convenient list of the possible outputs,
>either.
>
>And it would of course be yet another little bit of time per attachment.
>--
>Nick Phillips -- nwp at lemon-computing.com
>This will be a memorable month -- no matter how hard you try to forget it.

Maybe the original poster was just after something like:

If the attachment is on the list of disallowed file types, remove the
current extension (e.g. .avi) and replace it with .txt, which the recipient
could easily change later once they are sure the attachment is safe.  Seems
to me like this could be done pretty easily and would be a middle of the
road for people not wanting to totally block the attachment but at least
prevent the "click and execute" danger.

--Mike