Bug#989122: exim4: takes 10 seconds to accept connections after waking up on another network

[Rémi Letot]

Package: exim4
Version: 4.94.2-5
Severity: normal

Dear Maintainer,

when I put my laptop to sleep, then wake it up on another network
(which is what happens 95% of the times that I put it to sleep),
exim takes 10 seconds to accept any connection until I restart it.

Demonstration:

hobbes at sphax:~$ date && swaks --output /dev/null --to remi at lybrafox.be --server localho>
mer 26 mai 2021 11:14:09 CEST
mer 26 mai 2021 11:14:19 CEST
hobbes at sphax:~$ sudo service exim4 restart
[sudo] Mot de passe de hobbes :
hobbes at sphax:~$ date && swaks --output /dev/null --to remi at lybrafox.be --server localho>
mer 26 mai 2021 11:14:32 CEST
mer 26 mai 2021 11:14:32 CEST

I waited a bit before doing those tests, to be sure that the laptop
was fully awake.

If I don't redirect the output to /dev/null, I can see that the delay
happens in the very early stages of the connection, before any smpt
happens.

Thanks,
-- 
Rémi

-- Package-specific info:
Exim version 4.94.2 #2 built 17-May-2021 15:45:00
Copyright (c) University of Cambridge, 1995 - 2018
(c) The Exim Maintainers and contributors in ACKNOWLEDGMENTS file, 2007 - 2018
Berkeley DB: Berkeley DB 5.3.28: (September  9, 2013)
Support for: crypteq iconv() IPv6 GnuTLS move_frozen_messages DANE DKIM DNSSEC Event I18N OCSP PIPE_CONNECT PRDR SOCKS TCP_Fast_Open
Lookups (built-in): lsearch wildlsearch nwildlsearch iplsearch cdb dbm dbmjz dbmnz dnsdb dsearch nis nis0 passwd
Authenticators: cram_md5 plaintext
Routers: accept dnslookup ipliteral manualroute queryprogram redirect
Transports: appendfile/maildir/mailstore autoreply lmtp pipe smtp
Fixed never_users: 0
Configure owner: 0:0
Size of off_t: 8
Configuration file search path is /etc/exim4/exim4.conf:/var/lib/exim4/config.autogenerated
Configuration file is /var/lib/exim4/config.autogenerated
# /etc/exim4/update-exim4.conf.conf
#
# Edit this file and /etc/mailname by hand and execute update-exim4.conf
# yourself or use 'dpkg-reconfigure exim4-config'
#
# Please note that this is _not_ a dpkg-conffile and that automatic changes
# to this file might happen. The code handling this will honor your local
# changes, so this is usually fine, but will break local schemes that mess
# around with multiple versions of the file.
#
# update-exim4.conf uses this file to determine variable values to generate
# exim configuration macros for the configuration file.
#
# Most settings found in here do have corresponding questions in the
# Debconf configuration, but not all of them.
#
# This is a Debian specific file

dc_eximconfig_configtype='satellite'
dc_other_hostnames='sphax'
dc_local_interfaces='127.0.0.1 ; ::1'
dc_readhost='lybrafox.be'
dc_relay_domains=''
dc_minimaldns='false'
dc_relay_nets=''
dc_smarthost='mail2.lybrafox.be::587'
CFILEMODE='644'
dc_use_split_config='false'
dc_hide_mailname='true'
dc_mailname_in_oh='true'
dc_localdelivery='mail_spool'
mailname:lybrafox.be
# /etc/default/exim4
EX4DEF_VERSION=''

# 'combined' -	 one daemon running queue and listening on SMTP port
# 'no'       -	 no daemon running the queue
# 'separate' -	 two separate daemons
# 'ppp'      -   only run queue with /etc/ppp/ip-up.d/exim4.
# 'nodaemon' - no daemon is started at all.
# 'queueonly' - only a queue running daemon is started, no SMTP listener.
# setting this to 'no' will also disable queueruns from /etc/ppp/ip-up.d/exim4
QUEUERUNNER='combined'
# how often should we run the queue
QUEUEINTERVAL='30m'
# options common to quez-runner and listening daemon
COMMONOPTIONS=''
# more options for the daemon/process running the queue (applies to the one
# started in /etc/ppp/ip-up.d/exim4, too.
QUEUERUNNEROPTIONS=''
# special flags given to exim directly after the -q. See exim(8)
QFLAGS=''
# Options for the SMTP listener daemon. By default, it is listening on
# port 25 only. To listen on more ports, it is recommended to use
# -oX 25:587:10025 -oP /var/run/exim4/exim.pid
SMTPLISTENEROPTIONS=''

-- System Information:
Debian Release: 11.0
  APT prefers unstable
  APT policy: (500, 'unstable'), (1, 'experimental')
Architecture: amd64 (x86_64)
Foreign Architectures: i386

Kernel: Linux 5.10.0-6-amd64 (SMP w/4 CPU threads)
Kernel taint flags: TAINT_WARN, TAINT_OOT_MODULE, TAINT_UNSIGNED_MODULE
Locale: LANG=fr_BE.UTF-8, LC_CTYPE=fr_BE.UTF-8 (charmap=UTF-8), LANGUAGE not set
Shell: /bin/sh linked to /bin/dash
Init: systemd (via /run/systemd/system)
LSM: AppArmor: enabled

Versions of packages exim4 depends on:
ii  debconf [debconf-2.0]  1.5.76
ii  exim4-base             4.94.2-5
ii  exim4-daemon-light     4.94.2-5

exim4 recommends no packages.

exim4 suggests no packages.

-- debconf information:
  exim4/drec: