A few days ago I decided to upgrade the packages on my Lucid VPS and today I noticed that there is a queue of unsent messages on my VM host with “Service unavailable” response from my mail relay on the VPS host.

Upon closer examination I found that the mail log was full of:

Nov 18 06:45:25 yankee postfix/smtpd[25869]: warning: connect to Milter
service inet:localhost:8891: Connection refused
Nov 18 06:45:25 yankee postfix/smtpd[25869]: NOQUEUE: milter-reject: CONNECT
from unknown[2a01:d0:801a:1::12]: 451 4.7.1 Service unavailable - try again
later; proto=SMTP

What happened is I got a new opendkim package (2.6.8-0ubuntu1~ubuntu10.04.1) which listens on a unix domain socket by default, and not inet interface which I had configured for the filters.

The fix was to update /etc/opendkim.conf and add this:

Socket          inet:8891@localhost

Alternatively, this can be configured in /etc/default/opendkim:

# Uncomment to specify an alternate socket
# Note that setting this will override any Socket value in opendkim.conf
#SOCKET="local:/var/run/opendkim/opendkim.sock" # default
#SOCKET="inet:54321" # listen on all interfaces on port 54321
#SOCKET="inet:12345@localhost" # listen on loopback on port 12345
#SOCKET="inet:12345@192.0.2.1" # listen on 192.0.2.1 on port 12345

This took a while since I could not recall how I configured opendkim to listen to tcp socket in the first place. At least now it is obvious.