Question : Understand Smart host and Exchange server

I have very less knowledge on SMTP and how the routing works. (No idea about smart host at all). Need to understand the following:

We have a Web server (Windows 2003 with IIS 6.0).
And we have an MS Exchange 2003 server at a different site.

We have websites hosted in the web server which generates emails for external clients.
In the IIS - SMTP, Smart Host is configured with some IP address specified in it.

I need to understand how the emails generated from the website are routed.
Please specify what is a smart host IP. Is it the same as the Exchange Server IP? Or is it another intermediate server. What IIS does when it receives the email from the website.

Please give me a brief description on how the routing works in this scenario.

Answer : Understand Smart host and Exchange server

A smart host can be 'any' type of SMTP server this includes Microsoft SMTP. Te smart host will then relay the email on to its destination. As I said before this is to avoid possible problems with reverse DNS looks ups etc which result in the email being tagged as spam.
If exchange is being used for your company domain email... which i suspect it is, then all the DNS and reverse lookup and things to prevent spam taggin will already be in place pointing to that exchange server. So the web devlopers will be using the Exchange server as a smart host to be able to provide a more reliable less spammy looking email.
If your using exchange for your company email then it makes 100% sense to use your server to relay emails for yourcompany.com instead of sending directly from the SMTP server on the web server.
Your exchange server may not even be involved... it really depends on what IP the SMTP server is using as its smart host. If that IP matchs that of the external IP of your exchange server or not.