[bernardopires]

"There is no data. WhatsApp just passes the encrypted communication from your phone to another phone and that's it. It doesn't hold it."

That's not true. If the user receiving the message is not online how is the message supposed to be delivered? Obviously the server holds it until the user comes online. So yes, there is data.

[Nadya]

No comment about how secure the below is, but it seems trivial to not need data on the message itself.

The only data that needs to be stored by WhatsApp is `Sent` and not the message itself, which can be stored locally by the Messenger.

[Messenger] <--> [Sent Succesfully?] <--> Recipient

When the Recipient receives a message - they alert WhatsApp that the message has been received which can then alert the Messenger that the message has been sent. If it comes back with a failure, the Messenger will attempt to send the message again in `${Time}` until it sends. The message itself never has to hit WhatsApp's servers.