Emails are not been saved, received nor be sent

[torusturtle]

I installed ISPConfig on Ubuntu Dapper.
Everything looks good. I can connect to the server, send emails (which arrive at the receiver) or check for new emails.

Problem is that incoming mails are not being received or saved. /var/log/mail.log doesn't show an error.

Is there another log file that could lead to the problem?

I'm using Maildir by the way.

Thanks for your help!

[torusturtle]

Because this error occurred only with a few mailboxes I deleted and recreated them in ISPConfig. Now it works.