The other person isn't notified either way
Blocking or unblocking someone through this list doesn't send any notification to them β they may only notice indirectly, such as messages no longer appearing to fail.
Unblocking restores your existing chat history
Because the conversation itself stays intact while someone is blocked, unblocking them brings back the ability to message normally, with your previous chat history still there exactly as you left it.
Frequently Asked Questions
Will a blocked contact know I've blocked them?
No β blocking sends no notification, though the other person may eventually notice indirectly, like messages seeming to go undelivered.
Does unblocking someone restore our old conversation?
Yes β the chat itself is preserved while someone is blocked, so unblocking them brings your earlier conversation history right back.