Since the introduction of iMessages in iOS 5, you have had the option to turn on “Read Receipts” to tell your contacts when you have read their message to you (in Settings > Messages > Send Read Receipts). But it was all or nothing. Now in iOS 10 you can turn on read receipts for only specific recipients.
- Open a conversation with the person you wish to enable read receipts in the Messages app.
- Tap the encircled (ℹ︎) in the top right corner.
- Tap the slider for “Send Read Receipts”.
If you wish to turn it off in the future just visit the same place to slide “Send Read Receipts” off. Unfortunately there is not one central place to see who gets Read Receipts so you’ll need to go contact by contact.
Note: this property gets synchronized across all of your devices, which is great because you don’t have to worry about different devices communicating different things back to your contacts. But it also means that if you share an iCloud account with a significant other (not through iCloud Family Sharing but actually using the same login and password), you will likely be turning this feature on for all devices sharing that account.