How can I investigate why
make-network-process gets stuck forever?
I have been happily using mu4e as my mail agent for a number of years. After upgrading from emacs 24 to emacs 25 (at the same time as upgrading debian 8 jessie to debian 9 stretch, so it is possible that other factors are involved) I have lost the ability to send mail from emacs: after pressing
C-c C-c in a message buffer, the minibuffer displays
Trying <whatever> account...
essentially forever, without the mail getting sent.
t gave no joy (the
*trace of SMPT session to <host>* buffer remains empty and no messages appear), I managed to drill down to a call to
(make-network-process :name "smtpmail" :buffer #<buffer *trace of SMTP session to an.smtp.server*> :host "an.smtp.server" :service 25)
which gets stuck. At this point we cross the boundary from elisp to C, and I run out of ideas.
How should I proceed to diagnose and fix the problem?