Sieve destroys mail on redirection error

[Gary Mills]

We regularly run into this problem:  A user redirects their e-mail with
their sieve script to another address, but that address redirects it back
to them.  The result is that all e-mail sent to the user disappears
without a trace.  This happens because Cyrus does duplicate suppression,
so that the second time around the loop, the e-mail is discarded.  The
same thing happens if the user just redirects the e-mail to his Cyrus
mailbox.

This problem does not happen with sendmail aliases or .forward files,
for example, because sendmail inserts a `Received' header each time,
and detects loops by counting them.  Sendmail also eliminates duplicates
during alias expansion.

What can be done in Cyrus to resolve this problem?  Can mail loops be
handled differently than duplicate messages?  Can some notification be
returned to the sender?  Could the loop be broken by redirecting once
and delivering the second time?

-- 
-Gary Mills-    -Unix Support-    -U of M Academic Computing and Networking-
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