Which SMTP extension does Cisco ESA support for email security?

The STARTTLS (Start Transport Layer Security) command is a critical SMTP extension for email security. It allows an SMTP connection that starts as unencrypted plain text to be upgraded to a secure, encrypted connection using TLS. This process, often called opportunistic TLS, protects the confidentiality and integrity of email messages during transit between mail servers. The Cisco Email Security Appliance (ESA) fully supports and utilizes the STARTTLS extension as a fundamental mechanism for securing email transport, allowing administrators to enforce TLS for specific domains or offer it for all communications.

A. ETRN: This is an SMTP extension for remote message queue processing, allowing a client to request mail delivery from a server. It is a mail flow feature, not a security mechanism.
B. UTF8SMTP: This extension enables the use of UTF-8 characters in email addresses and headers for internationalization. It addresses character encoding, not communication security.
C. PIPELINING: This is a performance-enhancing extension that allows an SMTP client to send a batch of commands without waiting for a reply to each one, but it does not add encryption or security.

1. Cisco Email Security Appliance (ESA) Documentation: In the "Email Encryption" chapter of the Cisco AsyncOS for Email Security User Guide

the use of TLS for securing SMTP conversations is detailed. The guide states

"Cisco appliances use the STARTTLS extension to SMTP to create secure connections."

Source: Cisco AsyncOS 14.0 for Email Security User Guide

Chapter: Email Encryption

Section: How TLS is Used to Secure SMTP Conversations.

2. Internet Engineering Task Force (IETF) RFC 3207: This official standard defines the STARTTLS extension for SMTP. It specifies the mechanism by which a plain text SMTP session can be upgraded to a TLS-protected session.

Source: Hoffman

P. (2002). RFC 3207: SMTP Service Extension for Secure SMTP over Transport Layer Security. IETF. Section 2: The STARTTLS command.

3. Cisco Email Security Appliance (ESA) Configuration Guide: The configuration guides for Cisco ESA explicitly detail the steps for enabling and configuring TLS on public listeners

which involves managing the STARTTLS advertisement and policy.

Source: Cisco Content and Email Security Appliance Configuration Examples and TechNotes

Document: "TLS Configuration on the Cisco Email Security Appliance (ESA)". This document details configuring TLS

which is initiated via the STARTTLS command.