[Dovecot] new to dovecot

Hello all

I'm new to dovecot (and imap in general!) having installed only only today. My current set up is exim as MTA with procmail delivering /var/spool/mail/%user (which gets nfs exported). We also have a pop3 server running as well. I'm moving to new machine and though I'd look at dovecot and squirrelmail.

In /etc/dovecot.conf I'm confused by the default_mail_env, what exactly are we trying to set here? We have $MAIL set already, so for example what does the line:

default_mail_env = mbox:~/mail/:INBOX=/var/mail/%u

try to set

Cheers John