How to request confirmation on reception?
This function you can set when writting a message. You have to check "Request a read receipt" from the drop down menu "More" placed in the same row with the button "Send message":
After recipient opens Your letter, a small window appears, asking recipient whether he wants to notify you about receiving it.
If recipient will choose yes, You'll automatically receive e-mail notification about it, including such information:
If you were unable to find answer for your question, please write to firstname.lastname@example.org