37.21 Retrieving Mail from Local Mailboxes in Various Formats
If your incoming mail is stored on a local machine in a format other
than UNIX mailbox, you will need the mailutils movemail
to retrieve
it. See Movemail, for the detailed description of movemail
versions.
For example, to retrieve mail from a maildir
inbox located in
/var/spool/mail/in, you would set the following in Rmail inbox list:
maildir://var/spool/mail/in