If you don't have a fully-fledged MTA running on your local system, but would like to relay mail through the Pobox SASL servers, you might want to have a look at
ssmtp. You may find this especially useful in conjunction with using mutt to connect to your Mailstore account.
The following guide describe configuring
ssmtp in some depth:
ssmtp with Pobox, use the following settings:
AuthPass=Your Pobox Password