Pointofmail.com

Pointofmail.com is a new web service that you can use in order to know exactly who is reading the emails and attachments you are sending out. You can also know where they were read, for how long and it they were forwarded.

Moreover, Pointofmail.com will let you modify emails after they have been sent. That is a great option and no mistaking. If you have to send a report to your boss and you realize you have forgotten to attach it the minute you send the email out, then there is no need to panic. This application will let you undo the wrong, and avoid looking completely unprofessional.

Pointofmail.com works with all email addresses, and it also supports virtually any email client that you could think of. And while you are not required to download anything in order to begin using it, a set of optional add-ins is featured.
Again – all the main email clients and browsers on the market today are fully supported.