The read receipt only tells you that the recipient marked the message read. Neither receipt option will guarantee you that the message was placed in the Inbox or read. Not all email clients can return read receipts and recipients usually have the option to not return one. Read receipt: send a notification mail when email has been opened by the recipient.Delivery receipt: send a notification mail when the email has been delivered to the mailbox.If you are not familiar with receipts (because Outlook for Mac did not support it), receipts are notification that the message was received or read.

The option to request read and/or delivery receipts is on the compose mail Options ribbon and Draft menu.