When migrating mailboxes from an IMAP server, the read receipts for every mail in that account get sent without a question whether to do so.
So every email that was sent to me in the last 10 years that has a read receipt get answered automatically!
I receive emails why i send a read receipt for a 5 year old mail, this is very unwanted as i am about to migrate 250 mailboxes from the old mailserver and this is behaviour i don't need!
I have the option in the settings disabled for the read receipts.