Re: [Exim] Mail Loop with Null Senders and Oracle WorkFlow

Hi Kevin, on Sat, 31 Jan 2004 16:12:54 -0700 (MST) you wrote:

> Last week we had the fun of having a mail loop that was caused by the
> use of a Oracle Workflow mailer and any bounce message sent back to it.

I can sympathise! Just in case anyone else is having problems (it's
happened to me in the last few days too, and is probably more likely at
the moment with the current tide of junk), the exact same thing occurs
with Novell Groupwise, as I found this week. If a user sets an
"auto-forward" rule (not an unreasonable thing to do), it does indeed
forward it - but mungs the envelope sender to be the same as the Groupwise
*recipient*. Potentially infinite mail loop ahoy, if the forwarded message
gets rejected at any point beyond the first hop SMTP transaction. Grrrr.

I don't yet have an Exim rule to solve this; I've suggested to the
offending site which bombed me with their looping mail (who have Exim as
front-end MTAs) that they use a system filter to insert a unique "token"
header (e.g. "X-Flooble: Anti-loop") into locally-generated or received
bounces, and then again with the system filter (before the addition of the
header) check for that "token" in the message body of received/generated
bounces - if it exists, assume it's a loop and devnull it. It's not by any
means a perfect solution, and is a bad case of "fixing the symptoms not
the problem", but sounds like a possible relief to this kind of problem.

(If anyone from the offending ac.uk site is reading this, then hopefully
if/when they "solve" the problem they will be kind enough to post the
recipe here, for the benefit of anyone else in the predicament of having
broken mail-loop-causing software internally that they can't get rid of)

Tim