Fixing Postfix authentication issues on CentOS 6 with Virtualmin

The weirdest errors are those occurring on a freshly installed system where you’d expect for everything to simply work (with the default configs). But such new installs rarely work.

Roudcube successfully connects and sends emails through localhost. At the same time, external clients are unable to send emails through SMTP. The issues is…

Emails not visible on freshly installed CentOS 6 with Virtualmin

Main symptom of a problem is that emails are visible in the Read User Mail utility in Webmin but they do not show up in either webmail (Roundcube/Squirrelmail), Usermin or any email client configured to connect to the server.

After further inspection, it appears the emails get delivered to /var/mail/usermailbox@domain.tld instead of /home/username/homes/usermailbox/Maildir.