Whatever the reason is – or was – for you to use qmail and plesk, if you encountered even half my problems with qmail, you absolutely must get away from it. The Plesk-software however is a great invention! Even though it’s proprietary, it’s really helpful and convinient to manage a webserver, including domains and mail.
Unfortunately, I found myself forced to roll back my server a couple of times, because my mailserver qmail had stopped working without any error-message in the logs. Even more unfortunate is the person trying to resolve the problems with it – in this case: me. 
The only error-message you get is: “#421 unable to read controls”. All my hour-long attempts to change this, had no ultimate success. I rewrote config, changed permissions, restarted the service, backed up my mail and so on. All this, while knowing that no mail can be received by my server hosting about 15 Domains total.
When I found out, that Plesk could also work with postfix, I was thrilled! I envisioned switching servers down the road and the new server would run Postfix. What I didn’t know was how easy switching is using plesk. This is really the killer-feature to me right now! You just gotta love the simplicity. It preserves the email on the server and just switches the MTA to Postfix. Just perfect! So here you go:
Simply run:
/usr/local/psa/admin/sbin/autoinstaller –select-release-current –install-component postfix
Wait a few minutes… and that’s it!!!
For me, it saved my day! After hours trying to figure out how to fix qmail for the 100th time, the fix took a few minutes. Now the server is soaring and finnaly giving me good log-messages. Thank you, postfix. Thank you Plesk-develpers!
