Please let me know if this question belongs elsewhere.

I am wanting to setup a sendmail "gateway" for the purpose of running all incoming mail thru spamassasin or other tools on it's way into my exchange server.

Currently I answer port 25 at the firewall on a public IP that answers to mail.mydomain.com which is listed as my MX. The firewall forwards port 25 to my internal Exchange server.

From a DNS standpoint it should be pretty easy to have my Sendmail box (FreeBSD 5.3 - sendmail 8.12) answer as the MX, then forward on to the Exchange server as an A host, right? Or do I need to do some internal/external MX trix?

But that's getting ahead of myself, the real issue is I don't know how to configure sendmail at all, much less to make it what I want: A pass-thru gateway that scans every SMTP headed to my Exchange host and drops anything it doesn't like.

I'm not looking for an exact step by step, but after spending a day staring at sendmail doc's I was wondering if anyone had some general pointers to writeups of similar projects? And a handy dandy noob guide to configuring sendmail?

thanks!
-keith - uncre8tv@yahoo.com

Relyaing all inbound e-mail to your exchange server is the easy part. Simply add a mailertable entry to /etc/mail/mailertable:Take your pick.

As for running a filter program like spamassassin against each inbound e-mail (prior to relaying), checkout "sendmail milter" using your favorite search engine. There are many available.

Also, once you configure sendmail to use the mailertable feature, it will relay *all* e-mail for mydomain.com to your exchange server. This is great!, until an e-mail arrives with a bogus address. Your exchange server will bounce this e-mail back to what will probably be a bogus return address. So its queues get clogged. To fix this annoying problem you will also need to configure sendmail to check whether or not the e-mail/mailbox exists on your exchange server prior to relaying. This can be done in one of two ways:

1) Statically - add each e-mail address/mailbox on your exchange server to /etc/mail/access2) Configure sendmail to issue an LDAP query against your exchange server to verify the e-mail address. Unfortunately, I don't have any examples of sendmail/LDAP, but if I remeber correctly, the sendmail site has some links on configuring sendmail to use LDAP.