Sometimes you would like to know when the recipient reads the email you send. In Google Apps, PB&J Water has a feature set where you can know when someone opens the email.
To use this feature, when you compose the email, click on the little arrow on the right hand corner on the bottom that says "more options." Next, click on "Request read receipt." Compose and send your email as usual.
When the recipient opens the email, Gmail will send the email to your inbox. When you open it, there's a message at the bottom of the email that is highlighted in yellow that says the message has been read.
Sadly, this only works from a computer, not a phone.
Give it a try!