What is the difference between ESMTPS and ESMTPSA in email headers?
Summary
What email marketers say8Marketer opinions
Email marketer from MXToolbox explains that STARTTLS enables encryption for SMTP sessions. The protocol is initiated in plaintext, then upgraded to a secure, encrypted connection. It explains that STARTTLS is preferred over legacy SSL/TLS connections.
Marketer from Email Geeks explains that in theory, ESMTPSA is more trusted because someone had to authenticate to the MTA to pass the message in, assuming the MTA isn't lying.
Email marketer from Reddit user explains that securing SMTP involves using TLS/SSL encryption. While they don't explicitly mention ESMTPS/ESMTPSA, their advice highlights the importance of secure email protocols, providing valuable context.
Email marketer from Stack Overflow explains that SMTPS (SMTP Secure) was a deprecated method of securing SMTP connections directly over SSL on port 465. STARTTLS is the current preferred method, operating on port 587 with the STARTTLS command upgrading the connection to TLS. It indirectly refers to what makes ESMTPS secure.
Marketer from Email Geeks explains that ESMTPS means TLS was used and ESMTPSA means TLS and AUTH were used.
Email marketer from AuthSMTP explains that protocols like SMTPS (Secure SMTP) enhance the security of email transmission by encrypting the content of emails to protect sensitive information from unauthorized access. It provides context to the security aspect relevant to ESMTPS and ESMTPSA.
Email marketer from StackExchange explains that the advantage of authentication is that only authenticated user can use the server to send emails.
Email marketer from MailEnable Forum explains that STARTTLS command is used after the initial SMTP greeting, upgrading an insecure connection to a secure one using TLS. This contributes to understanding how ESMTPS secures connections.
What the experts say2Expert opinions
Expert from Word to the Wise explains TLS (Transport Layer Security). The modern standard is opportunistic TLS using STARTTLS, where the mailserver announces that it supports TLS encryption.
Expert from Email Geeks confirms that internal handoff is ESMTPSA and the one from the MTA to the MX is ESMTPS.
What the documentation says6Technical articles
Documentation from Microsoft explains that STARTTLS (opportunistic TLS) allows an SMTP client and server to upgrade a plain text connection to an encrypted (TLS or SSL) connection. This relates to the TLS component within ESMTPS.
Documentation from IETF explains about various RFCs regarding email transport security, which directly relates to the use of TLS with SMTP for secure communication.
Documentation from RFC Editor explains that Extended SMTP (ESMTP) extends the Simple Mail Transfer Protocol (SMTP) by defining a framework in which new extensions to the protocol can be easily defined. It does not define ESMTPS or ESMTPSA directly but lays the groundwork for understanding the extensions to SMTP that make TLS and AUTH possible.
Documentation from RFC Editor defines an extension to the SMTP service whereby a client may authenticate itself to the server, relating to the 'A' in ESMTPSA. It doesn't directly define the term ESMTPSA.
Documentation from RFC Editor explains the use of Transport Layer Security (TLS) with SMTP. This document doesn't explicitly use the term ESMTPS but defines how a secure SMTP connection is established. This relates to ESMTPS as it is the TLS part
Documentation from cPanel explains that SMTP Authentication requires users to log in to the mail server to send email, which is relevant to understanding ESMTPSA and the AUTH component.