What Are the Current ESMTP Commands that ESA and CES Supports?

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Updated:May 18, 2020
Document ID:214630

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    Introduction

    This document describes the Extended Simple Mail Transfer Protocol (ESMTP) commands which are supported by the Cisco Email Security Appliance (ESA) and Cloud Email Security (CES).

    What are the Current ESMTP Commands that Cisco ESA and CES Supports?

    The ESA/CES supported commands are:

    • auth - used for SMTP Authentication if enabled.
    • data
    • ehlo
    • helo
    • help
    • mail
    • noop
    • quit
    • rcpt
    • rset
    • starttls - used for TLS negotiation if enabled.
    • vrfy (always return a '2xx ok' response)

    Any other commands, which are not supported, return a "500 #5.5.1 command not recognized" echo response. By default after 5 incorrect commands, the ESA terminates the connection with the message "421 Exceeded bad SMTP command limit, disconnecting."

    In order to use the commands on the ESA for verification purposes, log in to the CLI and telnet to the ESA's listener IP on port 25.

    C680.esa.lab> telnet 10.66.71.122 25

    Trying 10.66.71.122...
    Connected to 10.66.71.122.
    Escape character is '^]'.
    220 C680.lab.test ESMTP
    EHLO test
    250-C680.lab.test
    250-8BITMIME
    250 SIZE 10485760
    help
    214-The following commands are recognized
    214- auth data ehlo helo
    214- help mail noop quit
    214 rcpt rset vrfy

    Related Information

    Revision History

    Revision Publish Date Comments
    1.0
    16-Jul-2019
    Initial Release
    TAC Authored

    Contributed by Cisco Engineers

    • Mathew Huynh
      Cisco TAC Engineer
    • John Yu
      Cisco TAC Engineer

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