[Mimedefang] limiting nested mime multiparts

[Joseph Brennan]

>> The MaxMIMEParts looks only at total number of parts, not recursion
>> depth. Clam shouldn't use huge amounts of memory for recursive parts (I
>> can't see a reason why a 50-part message would take substantially
>> different amounts of memory depending on recursion structure.)

As I asked last week, how many parts would a legit message have?
Since then, thanks to a cooperative user, I have had the chance to
see a 62-part legit message.  The sender was forwarding a web page
with all of its graphic links included, so that the recipient would
not be contacting the web server when reading mail.  Part of me says
62 parts is ridiculous, but the goal of not informing some webmaster
about the recipient reading mail is worthy.

The problem we actually had has to do with recursion, a forwarding
loop where one side re-sent the previous message as an attachment.
When it gets somewhere well over 100, mail starts tempfailing.

We are setting $MaxMIMEParts = 100; at this time, as an indirect way of
limiting recursion.

Joseph Brennan
Academic Technologies Group, Academic Information Systems (AcIS)
Columbia University in the City of New York