[Mimedefang] Unintended consequences

David F. Skoll dfs at roaringpenguin.com
Wed Dec 27 15:12:55 EST 2006


Ben Poliakoff wrote:

> Yes, it's a lose-lose situation.  

> I see this issue fairly frequently at my site.  Many of our users have
> their mailers set to forward messages as attachments.  The most common
> victims are electronic receipts (i.e.  "Your Order with Amazon.com").
> I'd love to figure out a safe workaround.

There are two safe workarounds:

1) Forbid the use of Microsoft Windows.  That works for Roaring
Penguin.  It is unlikely to work for most installations.

2) If you see a MIME part of type message/rfc822, then rather than blocking
it, just rename it to something innocuous like "message.eml" and rebuild
the MIME message.  See "action_defang" in the mimedefang-filter man page.

I've heard rumours that if Windows cannot determine what to do with a
file based on the MIME type or file name, it actually looks at the
"magic values" in the file to determine the file type.  If this is the
case (I have no way of knowing), then the only safe workaround is (1).

Regards,

David.



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