Before you try this tip: Request and return read receipts are only available for Gmail in G Suite and must be turned on by your admin. This feature is not supported in gmail.com (consumer) accounts.
Here’s how to request a read receipt:
Receipt requests will be sent to every recipient in the To: and Cc: fields. It does not send a request to recipients in the Bcc: field.Once the message has been read you’ll receive an email telling you the date and time that your message was seen by the recipient.