How exactly can the PoW required to send a swift like message be used to secure the Ducknote network? Isn't the whole point of PoW competing to solve blocks to process transactions? How can out of network PoW contribute if they're not trying to make a block?
1. SWIFT like messages will be onchain messages.
2. Social messaging platform will be based on out-of-chain messages (like we have self-destructed messages in XDN)
3. Are you familiar with Bitmessage? They use pretty the same technique against the network flooding. To send message you need to perform PoW. In our case this will be CryptoNight that will be used for additional XDN blockchain protection. In other words, to send the message, you will need to submit PoW. To be very clear: take your smartphone, launch the XDN messaging app, write a message, press the send button, wait a few seconds (doing PoW), Profit!
EDIT: They "will try to make a block".