[Mimedefang] Greylisting++

[Jonas Eckerman]

David F. Skoll wrote:

> noticed any problems.  Although it's true that the subject is
> controlled by the MUA, in the normal use-case, an MUA hands the
> message off to an MTA that is responsible for delivering it, and it's
> unlikely that the MTA will mutate the subject.

We have had a few situations where this could have been a 
problem. Went like this:

User of First Class system sent us a mail. The mail was blocked 
by the greylist.

The First Class system was configured to retry each message three 
times, and did so in less than a minute. (Yes, it was *very* 
badly configured, but that's hard for the oprdinary user to fix).

User got a note that the mail didn't reach us (of course the 
First Class system help made sure that our rejection message was 
not included in that note).

The user simnply tried again. Sending a completely new mail. This 
mail got thrugh without problems.

This happened a few times with different local and remote users 
until someone told me about it and I contacted the admin of the 
First Class system in question.

(This has happened with two different First Class systems now, 
wich makes me wonder if it's a common configuration of that 
software.)

As long as only the mail and relay addresses are used, a manual 
retry by the user works fine for getting through a greylist, but 
if the subject is also used a manual retry might fail because the 
user doesn't copy the subject exactly (yes, I know that the users 
probably could have told the software to resend the message 
rather than create a new one, but they didn't...)

It's quite probable that this situation is so rare and has such a 
small impact that it is of no consequence at most systems, but 
here it has happened enough to make me wary of using the subject 
for the greylisting.

Regards
/Jonas
-- 
Jonas Eckerman, FSDB & Fruktträdet
http://whatever.frukt.org/
http://www.fsdb.org/
http://www.frukt.org/