SMTPDiag is a handy tool for tracking down SMTP based issues. I recently used in a newsgroup posting that was helpful along with a few other times at http://www.orcsweb.com. It is definitely one of those tools worth having if you have to troubleshoot email issues.
- Nice short article how to use SMTPDiag.
- Download SMTPDiag. It doesn't require an install so it can be copied to any machine.
Bernard Cheah posting is helpful also.