I am installing Postfix on my unmanaged VPS hosting machine and I am doing it first time ever. I followed the installation manual on Ubuntu site and everything looks all right except one tiny thing: I can’t send email using Telnet. Here is the response:

421 4.3.0 collect: Cannot write ./dfnBA9gfVO030273 (bfcommit, uid=0, gid=111): No such file or directory

I googled for an answer, but nothing useful came up so I tried to debug the problem myself. By looking into mail logs (/var/log/mail.log, found by examining /etc/syslog.conf) I found following strange response:

 start postfix/master[15758]: fatal: bind port 25: Address already in use

That means only one thing: there is another process listening on this port. Hmm, what could it be? Sendmail, perhaps. I uninstalled it, according to guides I was using, but it was still running.

It’s time to stop it and start postfix!

sudo service sendmail stop

sudo service postfix restart


Problem solved!