How to check that sent email has gone out from SMTP

My company is using Mailbee SMTP component for sending emails. They asked me to investigate how to know when the email has gone out from SMTP's server queue.

As i know, regular smtp process is following:

-Mailbee connects with SMTP server -Mailbee sends to the SMTP the recipient and body of email -The SMTP server puts the email to the sending queue -When its time to send the email, the SMTP server takes it from the queue and connects with target SMTP server -The SMTP server sends the email to the target smtp -the SMTP server removes the email from the sending queue.

I want to know the moment when the email has gone from the sending queue. I need it to set a flag in my internal database.开发者_如何学JAVA The flag means that the message has gone from my SMTP server.

What's the best way how to check it ?

Hi look at this article: http://www.iislogs.com/steveschofield/want-help-with-iis-smtp-service-please-enable-logging

it describe how to enable the SMTP log in your IIS