Question : Locking down Exchange in SBS 2003

Hello Experts

I'm trying to setup the Exchange server to only receive emails from the MxLogic servers.  I've menu crawled trying to find the right place to do that.  Can anyone help wit that?  I thought I had it right, but I completely cut off email and had to undo it.

Thanks.

Answer : Locking down Exchange in SBS 2003

Things learned today:
[1] My ISP has my site on a Windows 2000 server. (I thought it was Windows 2003.)
[2] Windows 2000 is not supported by Visual Studio 2010.
[3] According to  http://en.wikipedia.org/wiki/Windows_2000: "Over ten years after its release, it [Windows 2000] continues to receive patches for security vulnerabilities nearly every month and will continue to do so until 13 July 2010."
[4] The bloat factor is VERY nicely gotten around by switching to a Unix compile.

In the next 12 days, I need to migrate to a new server.  Guess which O/S will win my business?

Many thanks, jkr, for your ideas and insights.