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Updated:May 18, 2020
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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.
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