sieve redirect mail loop causing mail to be lost

[Stephen Grier]

Hi,

We are running Cyrus-imapd-2.1.11 with sieve and duplicate delivery
suppression. One of our users complained that they had not been
receiving mail. It appears that this is because he has set up a sieve
script with a redirect rule which redirects all his mail to himself (his
own email address).

As far as I can tell, his mail is initially delivered to his Inbox, at
which point lmtpd redirects the mail back via the MTA to his email
address. The redirected mail is delivered a second time, at which point
it appears that the mail is suppressed by Cyrus' duplicate delivery
suppression.

I have seen a few references to this behaviour on the list from a while
back, but I'm not sure if this problem has been addressed in 2.1.11 or
later. When a redirect rule redirects mail to the same mailbox in this
way, will this always result in mail being silently discarded?

Would this problem be solved by disabling duplicate delivery
suppression? I am slightly confused by the fact that lmtpd is not
actually logging that it has suppressed the message when this occurs.
Yet the messages never appear in the user's Inbox.

Obviously the user's sieve script is broken and I would expect it to
produce a mail loop, which our MTA should handle. But it is very likely
that other users will inadvertently redirect mail to themselves, and if
this is going to cause mail to be lost we may have to disable duplicate
delivery suppression.

-- 

Stephen Grier
Systems Developer
Computing Services
Queen Mary, University of London