Endpoint Protection

we are using the Symantec Multi-tier Protection Small Business Edition in our office and noticed someone is using our server as a mail relay server.  right now I have reduced the amount of outgoing mail by adding the suspected domain name in the content filtering rules in the Symantec Information Foundation mail security application.  Does the Symantec Multi-tier Protection Small Business Edition offer some sort of mail filtering to eliminate these hackers to use our server as a mail relay?

You should disable mail relay on your mail server. If you are working as an Open Relay you may be added to different Blacklists and mails from you (your company) will be classified as Spam a lot more often than it should.

if i disable mail relay, then all inbound emails are blocked even the legitamate emails.  any suggestions?

reconfigure your server so it won't be OPEN mail relay http://en.wikipedia.org/wiki/Open_mail_relay

What is your mail server.  Depending on the server you are using and how it is setup you will have different ways of securing it.

Are you using hosting or in house mail server?
What authentication method(s) are you using for authentication (outgoing SMTP auth)?

You should be able to configure your mail server to only accept mail from your local users, but that does not usually help with "remote users".  You would than create a rule for your VPN IPs.  And for anyone else, @ home for example, wanting to get their e.mail and not VPN in to the company...  Webmail over a secure pipe (SSL or HTTPS)...

All of these features and more should be part of any standard Mail Server...

Exchange 2003 SP2
in-house mail server

What authentication method(s) are you using for authentication (outgoing SMTP auth)? Where do I check this?

You should be able to configure your mail server to only accept mail from your local users.  I'm a bit confused here.  shouldn't I accept ALL incoming mail to my internal email accounts?

you may check this page for tips and tricks about exchange:

http://www.msexchange.org/

and this article may be helpful:

Understanding Relaying and Spam with Exchange 2000