Monitoring SMTP Relay server using hobbit

Hi

I have two Windows 2003 server which works as SMTP relay server.

What are the key parameter of the server should I monitor from Xymon.

I want to check certain parameters like

1. If the Mail server is accepting mails.
2. If the Mail Server is able to relay it to the next server.
3. Is my Mail relaying server free from open relaying and stuffs,

How could I achieve all these using Xymon? I have BBNT "An NT/W2K **CLIENT** for Big Brother System & Network Monitor Version 1.08d" on all the Windows 2003 servers.