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Jasen
Asked: 2017-11-23 16:02:26 +0800 CST

RFC for "Received: With ESMTPS"

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Email Received: headers often say "With ESMTPS" but this phrase seems to have no standard describing it.

is there an RFC for Protocol ESMTPS?

RFC5321 only lists SMTP and ESMTP

smtp

1 Answers

  1. Best Answer

    How about RFC3848

    Abstract

    This registers seven new mail transmission types (ESMTPA, ESMTPS, ESMTPSA, LMTP, LMTPA, LMTPS, LMTPSA) for use in the "with" clause of a Received header in an Internet message.
    ...
    The new keyword "ESMTPS" indicates the use of ESMTP when STARTTLS is also successfully negotiated to provide a strong transport encryption layer.

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