Your mutt will need to be compiled with IMAP support. Depending on your operating system or distribution, this may not be the default for your mutt package.
Recompiling mutt is outside the scope of this article; please see your operating system or ports vendor help documentation for more information.
You can check to see if your mutt is configured properly by looking at the output of mutt -v. You should see a +USE_IMAP flag.
To connect to Mailstore using mutt, add the following to your configuration file (typically .muttrc):
set imap_user="youraddress@pobox.com"
set imap_pass="Your Pobox Password"
set spoolfile={mail.pobox.com/ssl}
set folder={mail.pobox.com/ssl}
mailboxes {mail.pobox.com/ssl}
If you'd like to relay mail through the Pobox SASL systems using your local MTA, please see our Postfix or ssmtp configuration pages.