Aditya Garg [off-list ref] writes:

Add an option to allow users to specifically enable or disable
retrieving the Message-ID from the Outlook SMTP server. This can be used
for other hosts mimicking the behaviour of Outlook, or for users who set
a custom domain to be a CNAME for the Outlook SMTP server.

Helped-by: Junio C Hamano [off-list ref]
Signed-off-by: Aditya Garg <redacted>
---
v2: Replace tab with spaces in "outlookidtweak" => \$outlook_id_tweak,

Good eyes ;-)

+--smtp-outlook-id-tweak=(always|never|auto)::
+	Outlook servers discard the Message-ID sent via email and assign a
+	new random Message-ID, thus breaking threads.
++
+--
+- 'auto' will attempt to retrieve the ID from the server only if the SMTP
+  server is 'smtp.office365.com' or 'smtp-mail.outlook.com'.
+- 'always' will attempt to retrieve the ID from the server irrespective of
+  the SMTP server being used. Use only if Microsoft is your email provider.
+- 'never' will disable this tweak irrespective of theSMTP server being used.

It is a shame that this is not just a simple boolean.  Those who
expect 'true' to kick in would be disappointed to find that their
'true' means the same thing as 'auto'.

If I were designing this feature, I would rather make it say:

    --[no-]outlook-message-id-fix::

	Outlook servers [DO THIS].  Giving this option reads the
	message-id assigned by the Outlook server and use it as the
	In-Reply-To message ID for subsequent messages.  Without the
	option, connections to only ... and ... automatically gets
	this tweak.  Pass `--no-outlook-message-id-fix` to disable
	the fix even for these hosts.

and make the implementation behave that way.

Note that this is a command line option that is specific to
git-send-email, so I omitted "smtp" from the name and instead
replaced 'id' with 'message-id' to make it more explicit what
gets munged.

But I do not care too deeply either way.  Let me queue the patch
as-is for now.

Thanks.