Add a Read Receipt to your mails
You can add a read receipt to your emails from the Settings menu.
Your Google Apps administrator will need to set this and it is an organisation wide setting. In the gApps control panel, go to Settings > Email, and turn on Read Receipts. You can choose to turn on receipts for just internal email addresses, maintain a list of external addresses that can have read receipts requested, or switch them on for all addresses. Once this is switched on, users will see a choice "Request read receipt" under the To: line.
Tip Update: In the new compose, Read Receipts can be found under the down arrow icon, bottom right of the compose window.