postfix only listens on localhost (127.0.0.1)
On a newly installed VPS (Parallells Virtuozzo) running Ubuntu 12.04 LTS I also installed postfix as my MTA. However, it turned out that it only listened on localhost. I checked that "inet_interfaces = all" in main.cf and that my /etc/hosts was up to date with my server’s hostname. The reason was that the machine had sendmail preinstalled and running.
A netstat -an gives:
tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN
To the solution to this is:
sudo /etc/init.d/sendmail stop
sudo update-rc.d -f sendmail remove
sudo /etc/init.d/postfix restart
Now netstat -anp show that postfix listens to all interfaces:
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 691/master