I have a mailbox setup on Exchange online in Office 365 which is polled by a POP3 client and all mail downloaded.
If that mailbox receives an email with a read receipt request, the read receipt is being sent automatically, even though when I log in to the mailbox with Outlook online, the settings for read receipts are set to never send a response, and under mobile settings, it's also set to never send a read request for devices collecting using exchange active sync.
This doesn't happen with other Office 365 mailboxes that I have setup when using the same POP3 client and the same configuration so I have no idea what is on this mailbox which would be causing this. Is there some other settings at exchange or mailbox level which might override what is set on the account settings?
There is nothing else accessing the mailbox apart from the POP3 client. I have checked under the security control panel in 365 that nothing else is accessing the account.