Alright, the data can be stored on IPFS, but where will the computations be carried out?
Beyond that, it depends on what you mean by "computations".
Our example is setting up decentralized email. What computation is needed to send and receive email?
1. You may mean the computation needed to encrypt and decrypt the emails. That would happen on your computer locally.
2. You may mean the computation to send and receive emails. I'm not sure how/where this would happen in this example. It might be on the blockchain somehow.
I'm curious about this as well so will be learning more about dapps (decentralized apps). Starting here
https://blog.chronobank.io/what-is-a-decentralised-applicati...
https://ethereum.org/en/developers/docs/dapps
For messaging dapps, check out the new Blockscan chat by the creators of Etherscan : https://decrypt.co/91226/etherscan-creators-launch-ethereum-... (note: NOT very decentralized yet)
This is past my level of expertise, but you could map out what those clock cycles of a mail server are going towards. For example, serving files, like we talked about, can happen on IPFS. No compute needed there beyond what IPFS already does.