Not sure about real-world statistics, but the current IETF position is that SMTP STARTTLS for mail submission (not transport) is to be phased out in favour of “

Not sure about real-world statistics, but the current IETF position is that SMTP STARTTLS for mail submission (not transport) is to be phased out in favour of “implicit” SMTP-over-TLS with no cleartext portion, due in part to the former being an implementation minefield[1]. [1] https://datatracker.ietf.org/doc/html/rfc8314#appendix-A https://datatracker.ietf.org/doc/html/rfc8314#appendix-A