Mailinfo

Mailinfo is an application that integrates with Microsoft Outlook and enables you to receive an alert when the emails you've sent have been opened.

How does it work? The program inserts a small code into your emails, which then alerts you the moment that they are opened. You will also be alerted when an email successfully arrives at its destination.

This way, you can find out exactly when your message was read, and how many times it has been opened.

Mailinfo could be very useful to let you know if any SPAM filters are intercepting your emails and keeping them from being received and read.