AFAIK Sendmail, which is the default on FreeBSD, does not support the Maildir format natively.It delivers mail to "/var/mail/person" files. So modifying sendmail's "main.cf" won't help you much.
See
http://en.wikipedia.org/wiki/Maildir
It has been ages since I used "procmail", but procmail transfers mail from "/var/mail/person/" to whatever you specify.
The big picture is as follows:
- Sendmail is the MTA, which receives mail and stores it in "/var/mail/person" files.
- Procmail is a delivery agent which distributes the mail in these "/var/mail/person" files.
- Dovecot is an IMAP server which allows users to log in to your box and read their mail.
My guess is that you use procmail to distribute the mail in "var/mail/person" files to the
"/var/mail/%u/Maildir" files so Dovecot can serve them via IMAP to your users.
Isn't there a utility or script to create Maildirs?