After a few days of tinkering, I have finally configured things on the linode vps account so it works and does pretty everything I need.
I am using Debian 4.0. Had thought about using Ubuntu, but decided to stick with Debian as I have used it previously in the same capacity, without it failing me.
On a previous setup where I had smtp virtual accounts in the usual directory structure of;
/home/vmail/${domain}/${user}/Maildir
I was always looking for a way to have a .procmailrc for the smtp virtual accounts, and finally after a bit of research I have managed to put something together that works. I cannot give much technical details apart from the fact I can now have procmail rules for smtp virtual mail users, and also have those users even have a custom .procmailrc file that will be honoured.