Best tool for Analyzing IIS 7 SMTP Logs

We tried going this route too, but relaying email can be quite difficult. After struggling with the Windows SMTP server for a couple months, we gave up and created an SMTP Proxy which we uploaded to CodePlex. You can use it for free and it is much simpler to use and maintain.

This is a technical query to resolve a social problem. Ask your e-mail server admin's for access to the log to prove that the e-mail was sent. Even adding a BCC to the outbound mail won't prove much, if it doesn't arrive, how do you know it didn't get eaten by some other server en route? You need to read your corporate mail server logs.

Or, at the very least, just subscribe to your own mailing list with a couple of e-mail addresses and see if you get the mail when the mail is sent to your users.