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The short

How can I investigate why make-network-process gets stuck forever?

The long

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.

After setting smptmail-debug-info to 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?

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  • 1
    Is a network connection to this server possible? Try: telnet an.smtp.server 25 from comandline like bash or cmd. If you do not get an answer from the server, then emacs is not involved. – jue Jul 13 '17 at 8:53
  • Indeed, I was going to try this, and never got around to it! The connection fails on the router I happened to be using, which seems to be using IPv6. Switching to a router that uses IPv4, the problem goes away. So the problem is indeed outside of emacs. – jacg Jul 13 '17 at 11:26
  • I closed this question because the comments indicate that the problem was not actually with Emacs, but with the network. – Dan♦ Jul 13 '17 at 14:17
  • I know this is old, but I want to share that I use a local postfix relay, and for the past several months I have been having issues sending mail. Most frequently I get errors sending email because it's unable to connect. Typically, I just keep retrying over and over, and after enough tries or time has passed, it goes. Mostly, I wanted to highlight that I have seen frequent issues doing smtp and given my configuration (local postfix relay) it's unlikely to be network related. – Nick Anderson Jan 11 '19 at 19:14
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Is a network connection to this server possible?
Try: telnet an.smtp.server 25 from command line (like bash).

If you do not get an answer from the server, then emacs is not the reason and you have to search for the problem in firewall settings, router settings, operating system or even hardware.

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  • As mentioned in the comment to the question, the problem was indeed external to Emacs. – jacg Jul 13 '17 at 16:08

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