can't create user output file

Hi All,

I have started to have email issues with some of our Virtual Domain clients.

Users in the same Virtual Server / domain are starting to get the following email bounce back messages:

<> (expanded from <>): can’t create user output file

Final-Recipient: rfc822;
Original-Recipient: rfc822;
Action: failed
Status: 5.2.0
Diagnostic-Code: x-unix; can’t create user output file

At first I thought it was due to disk quota issues, so I assigned an Unlimited disk quota to this Virtual Servers users, but the problem continues.

Any suggestions are greatly appreciated.