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Description
I'm evaluating moving Mantis issue tracker code (http://www.mantisbt.org) from phpmailer to Zend::Mail.
When notification mails are sent from a mantis installation, the Message-ID is set in such a way that subsequent mails coming from the same issue are threaded properly by email readers.
Right now, I can not find (neither in 1.5PR) any method for setting and getting the value of the Message-ID header, so this is clearly a blocker, at least in my use case.
Please evaluate and categorize/assign as necessary.