Who is sending this receipt confirmation if you open a message to read them?
It could be only the webmailer (gmail account) or the device app (aquamail)...who else...?
The receipt confirmation is always generated by the mail client of the receiver of the message in question. The mail client (a webmail app, thunderbird, Outlook) will deliver the receipt (open/read message) to the mail server and that server will deliver the notification to the mail account of the user who requested it.
A DSN (Delivery Status Notification) is something else and is generated by the first SMTP server that receives a message to notify that the message has been received correctly. This is something different.
EDIT :
ah I see that the notification was a forum notification and not a mail notification.