Bug#962847: exim4: takes forever to send a mail after sleeping

[Rémi Letot]

Marc Haber writes:

> On Mon, Jun 15, 2020 at 01:56:18PM +0200, Rémi Letot wrote:
>> My mail client and exim are both running on my laptop, and the provided
>> logs are from that same laptop.
>> 
>> The fault is the delay between exim accepting the message, and actually
>> delivering it to the smarthost. During that delay, my mail client is
>> stuck too.
>
> That is highly implausible. In a normal setup, the SMTP client is out of
> the game as soon exim has locally queued the message. Can you run
> tcpdump on lo to find out what's happening? I guess that you're putting
> the laptop to sleep before the (local) TCP session has been properly
> closed, making it subject to the exponential backoff algorithm and
> eventually a session timeout. There is not much exim can do in this
> situation.

nope, I'm not a developper but I know computers and networks, I don't
put it to sleep while it is delivering anything.

Besides, I had reverted to exim 4.93-16 since my last message, and have
not had any problem for several days. Now I upgraded again to 4.94-2 to
get a capture, and tadaaa, the delay is back. So it's definitely linked
to exim4.94, not to my usage pattern. (Now I agree with you, I can't
begin to understand how that delay can be directly linked to the sleep
time of the laptop, that's... interresting :-)

Events:

- wake my laptop
- test with 4.93-16, immediately delivered
- upgrade to 4.94-2
- send a test mail, immediately delivered
- pause to be sure that everything is done networkwise
- put the laptop to sleep
- wait about 20 seconds
- wake the laptop
- pause to be sure that everyting is done networkwise
- send a test mail, 20 secondish delay is there
- sudo tcpdump -i lo -w exim4.pcap
- send a second test mail
- the delay is there between 15:16:47.250804 and 15:17:04.667741

See attached capture. 


> Maybe it helps to force exim to actually queue messsages from lo instead
> of trying immediate delivery?

I just applied the default debian smarthost configuration, how do I
change that so that it queues the messages ? I think that this would
just hide the bug and delay, probably just give me my mail client back
but still delaying the actual deliveries. But I can try it for testing
purpose if you give me complete instructions.

Thanks,
-- 
Rémi

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