Virtual-mailbox-frontend is a project mainly written in Ruby, it's free.
This is a virtual mailbox frontend for managing virtual domains and mailboxes in any persistence store supported by postfix and dovecot (auth via SASL optional).
This is a web frontend, written in Ruby on Rails, using datamapper as ORM, for configuring virtual transport (domains) and users (mailboxes) for dovecot and Postfix, including support for SASL. You will find configuration examples in doc/examples.
It has been tested successfully with PostgreSQL 9.0 with pgcrypto on Debian Squeeze.