Moving from Qmail to Postfix

I'm migrating e-mail servers, changing from Qmail to Postfix along the way. These settings have been necessary so far:

/etc/postfix/main.cf:
   home_mailbox = Maildir/
   recipient_delimiter = -

The former sets up mail delivery for Maildirs (obviously), and the latter replaces the Postfix-style address separator of "+" (the plus character) with the Qmail-style "-" (dash, minus).

I've also updated .procmailrc to handle the address extensions that were formerly handled by dot-qmail files. Before, mail sent to adam-sample@sixohthree.com would be handled by ~/.qmail-sample. Now procmail will route these messages for me. First I uncommented the correct mailbox_command:

/etc/postfix/main.cf:
    mailbox_command = /usr/bin/procmail -a "$EXTENSION"

Then I updated my .procmailrc to handle extensions:

MAILDIR=$HOME/Maildir/
EXTENSION=$1

:0
* EXTENSION ?? ^^sample^^
$MAILDIR.SampleFolders/

The important bits are mapping the "-a" flag back to EXTENSION for readability, and the syntax of the matching line.