[mu4e bug] User-Agent header not set

[manphiz]

Describe the bug

It looks like mu4e doesn't set User-Agent header anymore. It used to do that when I was using 1.8.x. I stopped using it for a while and started trying it again since 1.12.5 and I can no longer see User-Agent being set. I suspect this may be happening for earlier versions as well.

How to Reproduce

Sending a mail and show all headers, and there is no User-Agent set.

Environment

Debian Linux stable (Bookworm)
Emacs 29.4
mu4e 1.12.6

Checklist

• you are running either an 1.10.x/1.12.x release or master (otherwise please upgrade)
• you can reproduce the problem without 3rd party extensions (including Doom/Evil, various extensions etc.)
• you have read all of the above

Possible Cause

'User-Agent is included in the draft header when message-newsreader is set[1]. However, the only place that it's being set is at [2] where it's let-bounded, so it has no effect on the code at [1].

[1]

mu/mu4e/mu4e-draft.el

Line 573 in f101e0d

,(when message-newsreader 'User-Agent)

[2]

mu/mu4e/mu4e-draft.el

Line 517 in f101e0d

(message-newsreader mu4e-user-agent-string)

[manphiz]

I have a tentative fix at #2751, though I'm not sure whether this is the best way to do this. Please advice. Thanks!