Upgrading to Debian Stretch with dovecot, postfix & opendkim

Debian Stretch is about to be released. I’m already upgrading some of my systems, and want to document a few issues I encountered after upgrading my mail server from Debian Jessie to Stretch.

Dovecot forgot what’s SSLv2

Before the upgrade, dovecot was configured to reject login attempts with SSLv2 & SSLv3. The corresponding line in /etc/dovecot/dovecot.conf looked like this:

ssl_protocols = !SSLv3 !SSLv2

After upgrading, logging into the mail server failed. Looking at the syslogs

dovecot: imap-login: Fatal: Invalid ssl_protocols setting: Unknown protocol 'SSLv2'

With the upgrade to Stretch and openssl 1.1.0, support vor SSLv2 was dropped entirely. Dovecot simply doesn’t recognize the argument anymore. Editing dovecot.conf helped.

ssl_protocols = !SSLv3

opendkim using file based sockets (Update 2017-10-13)

UPDATE - previous releases of opendkim on Stretch (v2.11.0) were affected by a bug, ignoring it’s own config file. See the Debian bug report.

The correct way to (re)configure the systemd daemon is to edit the default conf and regenerate the systemd config.

vi /etc/default/opendkim
# listen on loopback on port 12301:
systemctl daemon-reload; systemctl restart opendkim

Tell postfix to use the TCP socket again, if nessecary.

vi /etc/postfix/main.cf
# DKIM config
milter_protocol = 2
milter_default_action = accept
smtpd_milters = inet:localhost:12301
non_smtpd_milters = inet:localhost:12301
systemctl restart postfix

This should do it.

Before the upgrade, opendkim (v2.9.2) was configured as an initd service using loopback to connect to postfix.


SOCKET="inet:12301@localhost" # listen on loopback on port 12301


# DKIM config
milter_protocol = 2
milter_default_action = accept
smtpd_milters = inet:localhost:12301
non_smtpd_milters = inet:localhost:12301
root@host:~# systemctl status opendkim
opendkim.service - LSB: Start the OpenDKIM service
   Loaded: loaded (/etc/init.d/opendkim)
   Active: active (running) since Mi 2017-05-31 15:23:34 CEST; 6 days ago
  Process: 715 ExecStart=/etc/init.d/opendkim start (code=exited, status=0/SUCCESS)
   CGroup: /system.slice/opendkim.service
           ├─791 /usr/sbin/opendkim -x /etc/opendkim.conf -u opendkim -P /var/run/opendkim/opendkim.pid
           └─796 /usr/sbin/opendkim -x /etc/opendkim.conf -u opendkim -P /var/run/opendkim/opendkim.pid

During the system upgrade, opendkim daemon was reconfigured as a native systemd daemon, which meant /etc/default/opendkim and /etc/init.d/opendkim became obsolete, even though I was asked to install the new package maintainers version of /etc/default/opendkim.

Now the opendkim (v2.11.0) systemd daemon looked like this:

opendkim.service - OpenDKIM DomainKeys Identified Mail (DKIM) Milter
   Loaded: loaded (/lib/systemd/system/opendkim.service; enabled; vendor preset: enabled)
  Drop-In: /etc/systemd/system/opendkim.service.d
   Active: active (running) since Wed 2017-06-07 13:10:15 CEST; 23s ago
 Main PID: 4806 (opendkim)
    Tasks: 7 (limit: 4915)
   CGroup: /system.slice/opendkim.service
           ├─4806 /usr/sbin/opendkim -P /var/run/opendkim/opendkim.pid -p local:/var/run/opendkim/opendkim.sock
           └─4807 /usr/sbin/opendkim -P /var/run/opendkim/opendkim.pid -p local:/var/run/opendkim/opendkim.sock

I tried editing /etc/postfix/main.cf & adding the postfix user to the opendkim group to reflect the changes:

# DKIM config
milter_protocol = 2
milter_default_action = accept
smtpd_milters = local:/var/run/opendkim/opendkim.sock
non_smtpd_milters = local:/var/run/opendkim/opendkim.sock
root@host:~# adduser postfix opendkim

Restarting opendkim & postfix, the connection still failed to work.

postfix/smtpd[4451]: warning: connect to Milter service local:/var/run/opendkim/opendkim.sock: No such file or directory

Some research revealed that postfix does chroot its process to /var/spool/postfix (didn’t know that). To reflect this, I created new subdirectories and edited the systemd daemon.

root@host:~# mkdir -p /var/spool/postfix/var/run/opendkim
root@host:~# chown -R opendkim:opendkim /var/spool/postfix/var
root@host:~# systemctl edit opendkim
ExecStart=/usr/sbin/opendkim -P /var/run/opendkim/opendkim.pid -p local:/var/spool/postfix/var/run/opendkim/opendkim.sock

Note that the double ExecStart isn’t a typo.

After restarting all affected services, my sent mails were getting a valid DKIM signature again.

opendkim[11357]: OpenDKIM Filter v2.11.0 starting (args: -P /var/run/opendkim/opendkim.pid -p local:/var/spool/postfix/var/run/opendkim/opendkim.sock)
 2022 Jan Schumacher   •  Theme  Moonwalk