ProductiveMail

[admin]

ProductiveMail adds a small footer (image and text) to every message you send using the associated email accounts. Then, when the recipient opens the message, the image is automatically read from the ProductiveMail server, which in turn notifies the ProductiveMail viewer that the message has been read. The ProductiveMail viewer will inform you at all times the status of your messages: the date and time they were sent, the date and time they were opened (if already read) and the time elapsed between both events.

Also, you can use ProductiveMail without changing anything about the way you send your messages. You don't need to modify email addresses or compose your messages in another program. Simply associate your email accounts with ProductiveMail and that's it!