Check Email Delivery is a plugin for Nagios, the leading open-source network monitoring tool. It can also be used stand-alone from the command line.

Some typical uses of this plugin include:

Version 0.7.1b published 25 Feb 2012

OpenBSD port:
pkg_add check_email_delivery

FreeBSD port:
pkg_add -r nagios-check_email_delivery

This is what people are saying about Check Email Delivery:

Just grabbed your Nagios plug-in - just what I needed, thanks. Nice coding, too.
Great plugins!
Awesome... Thank you!
I was just about to develop a plugin along these lines, when I found that you saved me the trouble.
Thanks for your email delivery plugin. It is the best so far.
Thanks for all your work on this plugin it does make life easier!
I love this tool, it was flexible and easy to setup.
Thanks a lot for this great tool.
Real nice piece of code!
We use your check_email_delivery Nagios plugin suite extensively to ensure that mails actually get passed between the mail servers at our computing center.
I was just getting ready to write something along these lines myself and here we go, it's already done :-) Thanks a lot for your work!
Really good job!! Thank you very much.
Now I have the best of both worlds, server indexing and mail loop tests ;)
It is just the perfect tool.
Thanks for your great plugin, I am using it for years now and its working great