Outlook 2003 SP3 reusing Message-IDs

[Paul Gargan]

Hi,

We're running Outlook 2003 SP3 on Windows XP Professional, SP3. We're seeing
an issue whereby some installations of Outlook are reusing Message-IDs when
sending messages. Specifically, in certain cases, if a user replies or
forwards a message, Outlook sends the message using the Message-ID of the
original message, rather than creating a new Message-ID.

The email accounts are Cyrus IMAP. Our imap daemon has a duplicate
suppression feature which drops any message whose Message-ID matches the
Message-ID of an email previously delivered to the given recipient. So when
Outlook decides to reuse the Message-ID of old messages, the emails get
deleted instead of delivered.

We're not sure why it only happens some users and not others. The
Message-IDs in question all have the form <!&!xxxx..xxxx@domainname> where
the !&! at the start is constant and the xxxx... is a sequence of what looks
like Base64 characters. Anyone know what MUA generates these, or how to make
Outlook behave correctly when it sees them?

Thanks,
Paul.