HTC 10 User Manual page 126

126 Messages
Preventing a message from being deleted
You can lock a message to prevent it from being deleted even if you delete the other
messages in the conversation.
1. Open the Messages app.
2. Tap a contact (or phone number) to display the exchange of messages with
that contact.
3. Tap the message that you want to lock.
4. Tap Lock message on the options menu. You'll then see a lock icon for locked
messages.