By default it's TRUE (Non Zero), meaning we enforce the RFC2822 rule for MessageID.
If the Notes.ini parameter "RFC2822MESSAGEID=0" is used, then we revert back to the old behavior in R6, prior to this fix.
The 'RFC2822MessageID' setting will prevent Mail routing from compliance with RFC 2822. Beginning with Domino 6.0.4 and 6.5.2, the Mail router enforces the RFC 2822 rule that each Message ID is unique at all times. In prior versions of Domino, mail delivery failure reports had the same Message ID as the original mail. If RFC2822MessageID=0 in the NOTES.INI, then Domino reverts back to the old behavior prior to R6.0.4. The parameter was added to allow customers to revert to old behavior. Recommendation: Remove this setting from all NOTES.INI files. Using this parameter set to zero would result in mail delivery reports being noncompliant with RFC 2822 Restrictions: This setting exists in Domino 6.0.4 and 6.5.2 and beyond. Restarts: No restart necessary. Force the configuration change to be noticed by the router via the following server console command: tell router update config