[Dovecot] Failed to create storage with data

I am trying to setup dovecot with postfix and postgres. After I got dovecot connected to postgres and use Outlook Express to try to login, I have the following problem:

Jan 4 23:38:22 bluemountain imap-login: Login: chris [::ffff:192.168.1.2] Jan 4 23:38:22 bluemountain dovecot-auth: Login process 9 disconnected Jan 4 23:38:22 bluemountain imap(chris): Failed to create storage with data: /var/local/mail/mydomain.com/chris Jan 4 23:38:22 bluemountain dovecot: child 24616 (imap) returned error 89

The status of the directory /var/local/mail/mydomain.com/chris is 777, so I have no clue why it doesn't work.