FYI: Content-MD5(-Origin) hacks

[Richard Kettlewell <]

[Martin, I don't know if you're subscribed to anti-spam@localhost,
hence the CC.]

Martin Hamilton writes:

> <URL:http://www.net.lut.ac.uk/~martin/antispam/>
> 
> What's this ?
> 
>   Some hacks on widely used mail programs which let you suppress
>   duplicate copies of messages with exactly the same content.
> 
> Why ?
> 
>   This is a characteristic of lots of Bad Things, e.g. sp*m,
>   pathologically broken mail systems/gateways, and malconfigured
>   mail systems.

What do you propose to do about cases where legitimate messages are
sent more than once to the same host?  These can be generated in a
number of ways that I can think of:

 * CC'ing a message to someone on a mailing list that is also
   addressed by the same mail - one copy will go directly and the
   other via a list exploder, and the two copies will come in on
   different SMTP connections.

 * Sending a message to two people at different hosts one of whom has
   a .forward file redirecting the mail to the same host as the other.

Actually these two are special cases of the general problem where two
users at the same site are sent the same message by different paths.

 * Sending a message with Qmail, which AIUI makes a separate SMTP
   connection for every recipient of every message.

Of course you might choose to consider this behaviour "pathologically
broken".

ttfn/rjk