qq trouble in home directory (#4.3.0) Plesk 10

A recent problem appeared on my system, an emails address was refusing emails sent internally and a message was coming back immediately (if using a mail client like Kmail or deferred if using a webmail service like Gmail):

451 451 qq trouble in home directory (#4.3.0) (state 17)

Searching for this problem on Google does not return much. however I tried to do the steps of switching from Qmail to Postfix based on BStar’s Code Snippets experience.

After changing from Qmail to Postfix, I could not do the reverse immediately (Plesk install returned an error I was using the CP)

This changed the problem to state that the mailbox was full. Yet funnily enough the recipient in question had no Mailbox, only a redirect.

In the end I had to remove the mail account and re-create it as before. since then all is back to normal.

I also managed to switch back to Qmail using the CP afterward.