[Mimedefang] Watermarking locally submitted messages [was: Mimedefang/logwatch interaction]

[Philip Prindeville]

I was looking at the contents of mimedefang-ip-key, and
wondering if having MdF-awareness in submit.mc (.cf)
of the form:

Fx/etc/mail/milter-watermark


where milter-watermark is an MD5 digest of some local
data that is hard to guess...  but generates a unique
fingerprint.

Then have:

HX-Milter-Watermark: $x


And then in filter_begin() we could test for the
presence of this line, if it's present and contains
the correct value, then we accept the message with no
further filtering...

But in any case, we always do a:

action_delete_header('X-Milter-Watermark');

to avoid leaking this information out from this or
any other host...

-Philip