Explore WhatsApp Clock Sign, Single Tick, Double Tick

"WhatsApp follows a ‘store and forward’ mechanism for exchanging messages between two users. When a user sends a message, it firstly travels to the server of WhatsApp where the message is stored. Then server repeatedly requests the receiver to acknowledge receipt of the message. As soon as message is acknowledged, server drops the message which means it is no longer available in database of server. WhatsApp server keeps the message only for 30 days in its database when it is not delivered to receiver (when receiver is not active on WhatsApp for 30 days)."