A delivery receipt confirms delivery of your email message to the recipient's mailbox, but not that the recipient has seen it or read it. A read receipt confirms that your message was opened.
In Microsoft Outlook, the message recipient can decline to send read receipts. There are other scenarios where read receipts are not sent, such as if the recipient's email program doesn’t support read receipts.
What do you want to do?
Track all messages that you send
Click the File tab.
Under Tracking, select the Delivery receipt confirming the message was delivered to the recipient's e-mail server or Read receipt confirming the recipient viewed the message check box.
Tip: As a best practice, consider tracking only single messages of importance instead of all messages. Recipients who occasionally receive a notification that a read receipt is requested on your message are more likely to send a read receipt than if they are prompted every time that they receive a message from you.
Track a single message
In the message, on the Options tab, in the Tracking group, select the Request a Delivery Receipt or the Request a Read Receipt check box.
Track receipt responses
Open the original message that you sent with a request for a delivery or read receipt. This message is usually located in the Sent Items folder.
On the Message tab, in the Show group, click Tracking.
Note: Tracking doesn’t appear until at least one receipt is received. After you receive the first receipt in your Inbox, it might take several minutes before the Tracking button is available.