I believe proton does this on chain, but not lightning. I imagine they would be willing to implement the option if they could be reached

You can spin up your own mail server. AFAIK one can recister a domain name anonymously, and pay with lightning. The same is valid for the server (for example via lnvps). That gives you a 100% private email solution. Bonus: you get an unlimited number of email aliases.

https://esiliati.org/

Proton.me only thing is they accept only onchain, but they accept it themselves - without intermediary, so no KYC.

Proton. No LN just onchain.

For agents or not so important things there's https://lnemail.net/

If you use Tutanota’s free account, you can register without KYC, the recovery method is with key, you do not need to provide recovery email. But when you upgrade, they only accept credit card or paypal payments.

nostr:npub18q57qr3t07qljnapzqldaqa7ru2qwfpfnjdrwvhk327n3sc82f0qqwrs6f nostr:npub1mea2vwcu06qf7e4x00wd902vj54qnn2jacq76ldntrgfhtvhlpqqrvqane ?

Why would you not go with Monero? There are quite a few that qualify your question.

I've been loving proton.

You can purchase a vps for sats and run your own email server. Go federated protocols! (sarcasm)