I was struggling to wrap my head around how federated social media works until I realized that email has basically been doing the same thing for 30 years. Different email servers are like instances of a federated network. You can send emails to people from within a single server or you can send emails to people on any other mail server. Your email address is a username followed by an ‘@’ and the server address, just like on Lemmy. Email is a decentralized service I’ve been using the whole time!
No, encryption was considered. It was supported from pretty early on via PGP. If you check out decent mail clients (obligatory digdeeper), you’ll find the tooling.
Email with PGP is very far from secure. No forward secrecy (one mistake and the entire thread history is revealed) and metadata is unencrypted.
PGP email has nothing to do with the email protocol. All your message metadata and headers are still not encrypted/can’t be encrypted. You can only encrypt some payload with a PGP key, and it’s up to the receiver to figure out whether or not they want to trust any of the message metadata. The entire envelope is still plaintext everywhere. PGP email is just email, but you’re sending some random encrypted text in it.