bug#29427: Problem sending emails in message-mode after restart

[Emmanuel Boudreault <emmanuel.boudreault@polymtl.ca>]

Hello,

I seem to be having an odd bug sending e-mails. I've configured msmtp to
send e-mails. When I first send an e-mail in emacs, 'send-mail-function'
isn't defined, I get a prompt, I choose transport and everything works
as expected. The msmtp log shows that the from field is properly set to
'emmanuel.boudreault@polymtl.ca'. This keeps working until emacs is
restarted.

When I restart emacs, 'send-mail-function' is defined. When I try to
send an e-mail, it fails saying the From field is incorrect. When I look
at the From field in the msmtp log it shows that emacs generated a From
field even though there was a valid one in the e-mail header. The From
field is: 'manu@soma.i-did-not-set--mail-host-address--so-tickle-me'.
The 'send-mail-function' is set to '(quote sendmail-send-it)'.

I'm using emacs 25.3, using notmuch-message-mode. I've looked into the
elisp and it seems that the problem arises in the emacs message mode
(message.el) used by notmuch-mesage-mode. Any help would be appreciated.


Thanks for you time,
Emmanuel