Mailinfo 2.2.0 - Got It

You're on a game show and have to choose between three doors, only one of which guards the price. After you have made your choice, the host opens one of the remaining doors containing no price. Given the chance to change your selection, should you switch?
You should, and your chance of winning the price is then possibly higher than the chance of your emails getting delivered. At least there's a helpful Monty Hall for email, too:
Mailinfo is a particularly comfortable tool that lets you know when emails you have sent are opened — and if they are not. (Windows)