We encountered an issue with the received mails from the domain of one of our client particularly.

When a message is coming from this domain, it automatically got an ID message-ID=<null> instead of a classic ID like 184729 or something else.

When I take a look at the zimbra.log file, the mail passed normally through the different steps (postfix => Amavisd => status=sent) , but the recipient never receive the e-mail.

Then I take a look at the mailbox.log file, and this is what I see :
2009-09-09 17:13:58,253 INFO [LmtpServer-120] [ip=zimbra_local_ip_addr;] lmtp - Delivering message: size=3754 bytes, nrcpts=2, sender=user@client-domain.fr, msgid=<null>
2009-09-09 17:13:58,253 INFO [LmtpServer-120] [name=user@mydomain.com;mid=22;] lmtp - Not delivering message with duplicate Message-ID <null>

And it is the same for each mail from this domain. I restarted the server, so the first e-mail of this client arrive normally in the recipient mailbox, but each next e-mails encounter the same problem : Zimbra consider those as duplicated messages !! (because of the same ID=null)

I cannot set the zimbraMessageIdDedupeCacheSize parameter at 0, otherwise our mailbox will be spammed with a lot of duplicated e-mails (I checked this with the mailbox.log file).

How can I allow the duplicate message-id=null to arrive in the mailbox, or why and how can I do to not have message=null at entry of postfix ?

Please help, this is really urgent for us !

PS : ZCS 5.0.18 on an Ubuntu Server 8.04 fully updated