Why does the Cisco Email Security Appliance (ESA) use port 25 by default when opening telnet sessions and how do I specify a different port?

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Updated:August 7, 2014
Document ID:118195

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The Cisco Email Security Appliance (ESA) is a SMTP gateway appliance - it listens on port 25 by default.

The appliance can be configured to listen on another port for smtp traffic instead of 25. (GUI>Network>Listeners>Edit Listener>Port setting)

Should your appliance be listening for mail on a non-standard port, you can perform a telnet test specifying the optional port in place of 25. In our example below our mail host is listening on port 80.

In order to use a port other than 25 when using telnet to connect to a remote host, simply specify the port number following the hostname from the CLI:

esa.example.com> telnet mail2.example.com 80
Trying 172.19.0.94...
Connected to mail2.example.com.
Escape character is '^]'.

Alternately, the AsyncOS CLI will prompt you to enter a host and port if you simply enter telnet, then follow the prompts.

TAC Authored

Contributed by Cisco Engineers

  • John Yu and Stephan Bayer
    Cisco TAC Engineers.

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