I issued a receipt for reading. Why not show it?

The reason why I opened the read receipt is not displayed:

Maybe the other party has not turned on the read receipt function; Send the same information to multiple people. If a person does not open or refuse to receive the read receipt, the read receipt will not be displayed. After the mail is sent, it cannot be delivered in time due to network reasons, resulting in abnormal display of the read receipt; The recipient of the mail is forbidden to send the mail, resulting in abnormal display of the read receipt.

meaning

Receipt means that when the other party reads the email, the system will prompt the other party that "reading the email requires sending a read receipt, and the other party has not read it, so there will be no receipt reminder." QQ mailbox is a mailbox product launched by Tencent in 2002, aiming at providing users with safe, stable, fast and convenient e-mail service.

A receipt is a proof to the sender that an email has been delivered. It is stamped or signed by the recipient and sent back to the sender by the post office. Receipts and receipts; Know the attached part of the invitation, fill it out and send it back to the sender. Modern means to return an execution result to the requester by completing something.