On Wed, 25 Feb 2026, Dan Wing wrote:
One approach would be take idea of https://datatracker.ietf.org/doc/html/rfc8314 and extend it include SMTP itself, which would bring QUIC along doing a happy eyeballs-like attempt at QUIC falling back to TLS-over-TCP falling back to TCP-port-25-STARTTLS falling back to TCP-port-25 plaintext, or as Martin suggested have DNS optimize those choices.
The problem with that is that SMTP doesn't do the TLS handshake at startup, only after a STARTTLS command in the TCP session. But see next message.
R's, John
