I am setting up and testing what will be a multiserver environment with archiving for 5000 users. We will have a couple of external MTAs for encryption and AS/AV of internet mail. Internally we will have three mailbox servers, an LDAP master and an LDAP replica, two mtas and a server for archiving.
I am wondering about the MTAs. Should We bother with seperate servers for MTAs or just put an MTA on each of the mail stores? It seems having seperate MTAs would cause a little extra network traffic in and out of the mailstores when sending to mailboxes located on the same server.. the message has to go out the mailbox server and into the mta to be scanned, then back into the mailbox server to be delivered. If I had an mta right on the box it wouldnt have to leave the system at all.. I was planning on using a proxy server as well, but we may just use a bigIP load balancer..
Anyway, just an idea.