Virtualmin and SMTP Store and Forward


Hope someone can help, I am looking to use Virtualmin to host a number of domain names, 2 of which have mail servers already that host mailboxes. I need to accept mail for the domain from the internet and Spam and Virus check it on Virtualmin and then SMTP relay it to another server. The other server will except mail for the domain and will host the users mail boxes. (It will only accept mail from the Virtualmin server)

I also need the other domains to work as normal with Virtualmin hosted users and mail boxes.

Any help would be great,