By Lori Kaufman, HowToGeek.com, September 14, 2016
By default, iMessage sends a read receipt back to the sender, so they can see when you’ve read their message.
You can turn this feature off completely, but what if you want to send read receipts to some people but not others?
In iOS 10, you can now turn off read receipts within each conversation separately. Say you don’t want your mother-in-law to know when you’ve read her messages. You can turn off read receipts in the conversation with her, but leave the main setting on for everyone else.