You can’t have that. Big boys club issues aside with spam rankings there is no way to have encrypted and private e-mail. The SMTP protocol relies on message headers contained within the message.
The body might be encrypted but subject, sender, recipient, etc will be visible plain text to both MTAs handling your message delivery.
What Protonmail does is just encrypting the mailbox storage.
iru@localhost $_ /
npub1nm…42975
2025-03-19 22:48:40
in reply to nevent1q…98lx
Author Public Key
npub1nmk2399jazpsup0vsm6dzxw7gydzm5atedj4yhdkn3yx7jh7tzpq842975Published at
2025-03-19 22:48:40Event JSON
{
"id": "4527376e02de57dedc2db8e079bad798d91fda97cf3e5aa4f206eaf35997c893",
"pubkey": "9eeca894b2e8830e05ec86f4d119de411a2dd3abcb65525db69c486f4afe5882",
"created_at": 1742424520,
"kind": 1,
"tags": [
[
"e",
"ec72fb9d8960445156328d7b661a04097a20c98b4fe7163bf3f64de549775bc0",
"",
"root"
],
[
"p",
"3b7fc823611f1aeaea63ee3bf69b25b8aa16ec6e81d1afc39026808fe194354f"
]
],
"content": "You can’t have that. Big boys club issues aside with spam rankings there is no way to have encrypted and private e-mail. The SMTP protocol relies on message headers contained within the message.\n\nThe body might be encrypted but subject, sender, recipient, etc will be visible plain text to both MTAs handling your message delivery.\n\nWhat Protonmail does is just encrypting the mailbox storage.",
"sig": "fd9900a571732147ab146c35fd71c13a5101714db5da108f3bf2013be2651480a2d61a56d23facdd3eeae1ef2f59df466b843330b95aba6c732bd161c08ffec9"
}