Fix: Adapt to Gmail.

[liaosunny123]

Add Message-ID to the mail service header to adapt to services such as Gmail

[CLAassistant]

All committers have signed the CLA.

[HFO4]

Is there any document on why this field will affect Gmail?

[liaosunny123]

Is there any document on why this field will affect Gmail?

refer to https://datatracker.ietf.org/doc/html/rfc5322#section-3.6.4

Here:
Though listed as optional in the table in section 3.6, every message
SHOULD have a "Message-ID:" field. Furthermore, reply messages
SHOULD have "In-Reply-To:" and "References:" fields as appropriate
and as described below.

If you send email to Gmail with original settiings, you will got:
host gmail-smtp-in.l.google.com[xxx] said: 550-5.7.1 [xxx] Messages missing a valid Message-ID header are not accepted. For more information, go to https://support.google.com/mail/?p=RfcMessageNonCompliant and review RFC 5322 specifications.

[HFO4]

Thanks!