One of the advantages of the blockchain is that, unlike conventional Internet services, you do not have to maintain a backend in order to offer a service. You do however need to pay to write a transaction onto the blockchain. Message delivery is certainly something that can benefit hugely from the blockchain.
One of the potential use-cases for Ethereum is to create a fully decentralized Git. Git is already decentralized in many respects, but you still need to push/pull with a specific server. If something like Git was implemented on Ethereum you just need to connect to another Ethereum node on the network.