Works and not works, Why? "Message Delivery Receipts"
Example
Work 1/3
user1 (connect)
user2 send message user1
user2 (connect) receive from user1 (check receiv correct)
Work 2/3
user1 (disconnect)
user2 send message user1
user1 (connect)
user2 (connect) receive from user1 (check receiv correct)
Not work 3/3 ( This case is the best important ) user1(no internet) + user2(no internet) = never work check
user1 (disconnect)
user2 send message user1
user2 (disconnect)
user1 (connect)
user2 (connect) not receive from user1 (no check receiv correct)
When in facebook, you read a message, and then you disconnect, the other user is re To connect, you see that you have read the comment of mine
