Understand Supported SMTP/ESMTP Commands and Extensions

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Updated:July 1, 2026
Document ID:217162

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Introduction

This document describes the available SMTP/ESMTP commands and extensions on the Secure Email Gateway, formerly known as the Email Security Appliance.

Commands

If a command or extension is not listed here, or if you wish to obtain additional details, please reach out to Cisco TAC.

These are a few available commands on Secure Email Gateway:

  • DATA
  • EHLO
  • HELO
  • HELP
  • MAIL FROM
  • NOOP
  • QUIT
  • RCPT TO
  • RSET
  • VRFY

Extensions

Listed here are a few available extensions on Secure Email Gateway:

  • 8BITMIME
  • AUTH
  • SIZE
  • SMTPUTF8 (AsyncOS 14.0 and newer)
  • STARTTLS

Related Information

Revision History

Revision Publish Date Comments
2.0
01-Jul-2026
Recertification
1.0
27-May-2021
Initial Release
TAC Authored

Contributed by Cisco Engineers

  • Dennis McCabe Jr
    Cisco TAC Engineer

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