During my SMTP Relay setup, i noticed the Send email function is called successfully BUT no email is sent to my mailbox.

I check the following directory C:\inetpub\mailroot\Queue and noticed that there are a few EML file stuck in it.

After googling and troubleshooting, the problem is that in the IIS6 > SMTP’s Properties > Outbound Security, the Basic Authentication is specified with an invalid email address and password.

Update them and now my email will be sent out.