[CentOS] Large scale Postfix/Cyrus email system for 100,000+ users

> I thought the usual ways of doing this were to either use a 
> high-performance NFS server (netapp filer...) and maildir format so you 
> can run imap from any client facing server, or to keep the delivery host 
> information in an LDAP attribute that you find when validating the address.
> 

This is the 'I have the money' way of doing this ;-)