Sieve forwarding loop destroys e-mail

Joseph Brennan brennan at
Mon Mar 31 08:40:35 EDT 2008

Jo Rhett <jrhett at> wrote:

>  I would ask that you spend some time determining how the
> program could determine it is a bad rule, and provide a patch to fix this
> behavior.  (in short -- it's harder than you think)

A mail delivery system that loses mail is buggy.  I don't need to look
at the code to know that.

You can tell me no one has time to fix it, and in an open source project
I can respect that.  But it is a bug.

>  > or back to sender (grounds: not deliverable as configured).
> Only if you want to become a source for backscatter.

Losing mail is much worse than backscatter.  With bounces limited to
people who get a forward loop going, bounces are not a big issue.

Gary Mills <mills at> wrote:

>  Of course,
> it's impossible to distinguish between a forwarding loop and a real
> duplicate unless another `Received' header is added to the message
> header.

Hm.  What if duplicate suppression is turned off?  Infinite loop?

Hop count is the classic MTA method of detection, but here the very
first time around the loop will hit dup suppression.  This calls for
something else that lets the system know the message already passed
through a local sieve script.

Joseph Brennan
Columbia University Information Technology

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