Bug 1837680: Add Message-ID header when missing at send #146
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Detect whether a Message-ID header has been included in the message passed to MessageToMTA and generate one if it's missing.
GMail and other modern mail services now expect a Message-ID as part of the message else they mark them as spam or drop them entirely.
** This is a port of the same bug fix submitted for Bugzilla 5.2 **