What I do is set the
MAIL environment variable to point to my mailbox. That way the setting applies to other programs (e.g. shells that show “you have new mail”). But you can do it from
.muttrc as well:
set spoolfile = "/path/to/mailbox"
To start mutt showing a different mailbox as a one-off, run
mutt -f /alternate/mailbox. Within mutt, type
c to change to a different mailbox. After
c, you can type the path to the mailbox, or you can use one of the shortcuts (see “Mailbox shortcuts” in the manual) such as
! to refer to
=foo to refer to
$folder is defined in your
set spool = "/path/to/directory/containing/mailboxes"
If receive mail in several mailboxes and would like mutt to tell you when you receive mail in any of them, look up “Monitoring incoming mail” in the manual; basically you need to add this to your
mailboxes "/mailbox/to/watch" "/other/mailbox/to/watch"