Question : SMTP Server in the DMZ

Hi,

I am currently trying to brainstorm for a client of mine how they should move forward with thier mail infrastructure.

The main objective is to provide a more secure environment than at present (1 exchange server which has all SMTP inbound traffic routed from the firewall to it and also holds all mailboxes for internal clients).
I have suggested they setup a DMZ and place an SMTP server there as the first port of call for all inbound mail connections. I have also suggested they implement some form of content filtering/AV/anti-spam at this point also to reduce the amount of unnecessary email entering the internal mail server(s).

What i wanted to post to everyone was the question of how would i best implement a 2 part mail system.
1. DMZ mail server
2. Internal Exchange Server(s)

And which products for the DMZ server have people used in the past.

Thank You.

Answer : SMTP Server in the DMZ

For DMZ mail relaying server, i would use either sendmail or qmail since these products are reliable for smtp routing.  Some people also suggest postfix but I personally never use it before.   Sendmail, qmail can easily be configured on linux based system.  It's cheap so you should consider set up redundancy with at least two DMZ mail relaying by adding another MX record for the second smtp server in case the first one goes down.  This also helps for load balancing

It depends on how complicated your e-mail network infrastructure, you can even set up the similar mailhub inside your firewall.  In my environment, we have a huge mixed e-mail infrastructure with exchange, openexchange, sendmail with POP and IMAP, and Netscape Messanging server.  So, i set up a pair of mailhub using sendmail.  All internal mail are relaying through these mailhubs with the alias file pointing the recipient to the right destination e-mail servers.  All outgoing mail will be forwarding out directly.  

Incoming Mail:  Internet --> DMZ smtp server --> Internal smtp mail hub --> mail server
Outgoing Mail:  mail server --> internal smtp mail hub ---> internet

hope this will help.
vayoha