The creating a postmaster account part is easy.
From the control pannel, go to “mail”, then “manage addresses”. Click "Enter a Enter a new address, using “postmaster” as the name. Click the “Create a new email address” link.
In the “Email sent to” field, put in postmaster
Click the “will be delivered to these email addresses” radio button and enter the email address you want it delivered to (ie: firstname.lastname@example.org).
Take the check out of the box “deliver to this mailbox:” and hit the create button at the bottom.
If someone emails postmaster at your domain, it will now be delivered to the bo account.
Creating one for “abuse” is always a spiffy idea too.