[Dovecot] newbie - trying to set up pop3 access for multiple domains

I'm hosting multiple domains, and I'm having problems getting dovecot to play nicely.

The only protocol I've got enabled in the conf file is pop3, yet the maillog shows the following entries when I try to authenticate:

mbox: Can't create root IMAP folder /mail: Permission denied Failed to create storage with data: mbox:/var/mail/vhosts/<domain name here>/<user name here> returned error 89

Any ideas/suggestions would be greatly appreciated.