1. IANA Considerations
As directed by SMTP [2], IANA maintains a registry [7] of “WITH protocol types” for use in the “with” clause of the Received header in an Internet message. This registry presently includes SMTP [6], and ESMTP [2]. This specification updates the registry as follows:
o The new keyword “ESMTPA” indicates the use of ESMTP when the SMTP AUTH [3] extension is also used and authentication is successfully achieved.
o The new keyword “ESMTPS” indicates the use of ESMTP when STARTTLS [1] is also successfully negotiated to provide a strong transport encryption layer.
o The new keyword “ESMTPSA” indicates the use of ESMTP when both STARTTLS and SMTP AUTH are successfully negotiated (the combination of ESMTPS and ESMTPA).