About Postfix ...

[ephigenie]

no there's no particular reason to store mailboxes in mysql.
Although maybe we'll store the configuration in a database some day for easier handling.
SQL - Storage maybe only of relevance for people using a cluster of postfix/ imap/pop3 servers and then using the replication feature.

But atm i'd recommend to use NFS for that or a shared storage device with enbd/gnbd + ocfs2/gfs on it.

But for solution's of that size we've to develop the whole framework, first (ispCP) .
Thats nothing which will be managed directly in VHCS Omega.