The config file is well commented, but not matter how I spelled out the path for mail boxes it always wanted to use /var/mail as opposed to /var/spool/mail/ which seems more logical in general.
This should give you something close to the old UW-IMAP setup:
default_mail_env = mbox:~/mail:INBOX=/var/spool/mail/%u
However, I had to change my client (Mulberry) to use a hierarchy of "*" instead of "mail/*". But it's acceptable as I no longer have to worry about the server trying to treat the rest of my home directory as a mail archive.
It's also necessary to add pop3 and pop3s to the protocols setting.
