I'm writing up documentation and want to ensure that I'm using proper terminology.
1) What is the proper technical term for the SMTP tunnel encryption standard that typically starts on TCP/25, involves checking ESMTP capabilities for 250-STARTTLS and issuing the
STARTTLS command (followed by negotiation, public cert exchange, etc)?
2) Likewise, what is the proper technical term for SMTP tunnel encryption that uses port TCP/465 and requires negotiation immediately
I've always just called #1 "TLS Encryption"/"TLS" and #2 "Secure SMTP"/"SMTPS" but I don't think that's accurate.
STARTTLSas "opportunistic TLS encryption".
STARTTLSwhen sending to some domains but I don't think it is necessarily appropriate for all use cases of option 1. For example, what if I explicitly require the use of
STARTTLSwhen sending to bob.com?
STARTTLS... It is a way to upgrade a session to a secure channel, but if the other server doesn't support it, nothing happens, and there is no way of making the other party comply. Hence the "opportunistic" description.
TLS_Srv:secure.domain ENCR:112in sendmail which lets you require a minimum bit strength for a TLS session and defer the message if the other side doesn't have TLS or doesn't meet the minimum requirement. Details here: sendmail.com/sm/open_source/docs/m4/starttls.html