I believe mailbox.org let's you do the same (upload a private key with which all unencrypted mail will be encrypted). And they let you use it with your own doma

I believe mailbox.org let's you do the same (upload a private key with which all unencrypted mail will be encrypted). And they let you use it with your own domain. I think it's a great feature that more hosts should offer. Actual deniability, what's not to love?