When an email is sent from an Exchange mailbox, with a Delivery Receipt Request, the following line is added to the email headers:
Return-Receipt-To: <sender@domain.com>
When an email is sent from an Exchange mailbox with a Read Receipt Request, the following line is added to the email headers:
Disposition-Notification-To: Sender Name <sender@domain.com>
This is the standard mechanism by which Exchange sends Delivery and Read Receipt Requests. This mechanism does depend on the recipient email system honoring such requests. There is no way to force a recipient email system to do so. If you have access to any of the tests performed with the receipt requests, we recommend checking the headers of those emails to verify that the above lines are included. If not, then they may not have actually been enabled for those emails, or they were enabled and the email client did not append the lines as it should have.
The latter case may require some additional investigation to determine the cause. If the lines are present in the email headers, then the receipt requests were properly added to the emails on our side and the recipient side either failed to reply or does not support replies for the receipt requests.
