read-receipts & duplicate delivery suppression

[Stephen Grier]

Hi,

We're currently running cyrus-imapd-2.1.11 with duplicate delivery
suppression enabled.

We recently received a complaint from a user who reported not receiving
a message he was sent. On investigation, it seems that he initially sent
a message to a third party along with a request for a read-receipt. The
third party returned the read-receipt. It seems that when the third
party then replied to the original message, lmtpd suppressed it because
it contained a message-id identical to the one on the read-receipt sent
earlier:

Jun 10 15:23:31 machine lmtpd[15702]: duplicate_check:
<!~!UENERkVCMDkAAQACAAAAAAAAAAAAAAAAABgAAAAAAAAA23QMnm+cHU69O61NP8XnZKKEAAAQAAAAnIdE164vBE6gxAKZkS5UiAEAAAAA at microgenics.co.uk> user.XXXXXX         0
Jun 10 15:23:31 machine lmtpd[15702]: duplicate_mark:
<!~!UENERkVCMDkAAQACAAAAAAAAAAAAAAAAABgAAAAAAAAA23QMnm+cHU69O61NP8XnZKKEAAAQAAAAnIdE164vBE6gxAKZkS5UiAEAAAAA at microgenics.co.uk> user.XXXXXX         1055255011
...
Jun 10 15:56:45 machine lmtpd[17525]: duplicate_check:
<!~!UENERkVCMDkAAQACAAAAAAAAAAAAAAAAABgAAAAAAAAA23QMnm+cHU69O61NP8XnZKKEAAAQAAAAnIdE164vBE6gxAKZkS5UiAEAAAAA at microgenics.co.uk> user.XXXXXX         1055255011
Jun 10 15:56:45 machine lmtpd[17525]: dupelim: eliminated duplicate
message to user.XXXXXX

Has anyone else observed this happening? As far as I understand rfc-822
message-ids are supposed to be unique, but read-receipts are
non-standard, so I don't know if the client which did this, MS Outlook,
Build 10.0.3416, behaved sensibly or not. We may have to disable
duplicate delivery suppression if this is likely to happen again.

Thanks

-- 

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