On 1 Jan 2022, at 9:03, Keith Moore wrote: > On 12/31/21 6:04 PM, John C Klensin wrote: > >> Second, I'm not sure what you mean by "OpenPGP over SMTP" but >> cannot think of anything that would prevent defining an SMTP >> extension that asserted that no message was welcome unless the >> content was in OpenPGP (signed, encrypted, or both). > > You don't even need an SMTP extension to do that, you just need an SMTP server that can be configured to refuse or bounce mail that isn't signed and/or encrypted. I continue to think that the sender of a message containing potentially sensitive information is a better judge of its need for encryption than the recipient. The only example I can think of where it would be useful for the recipient to refuse unsigned/unencrypted content is a whistleblower mailbox, and then only to remind the sender to use those things, and then it’s probably too late because the message may already have been sent to an intermediate relay. I should probably point out RFC 8689, “SMTP Require TLS Option”, that allows the sender of a message to require that it be sent via TLS. Unfortunately there isn’t any operational deployment of REQUIRETLS, perhaps in part because it requires deployment of DANE or MTA-STS to make it secure against MX record spoofing attacks and the like. Those attacks would also need to be considered when discussing anything involving public key discovery through an SMTP option or command. -Jim
