Telnet Connections To The Smtp Port Number - Fortinet FortiMail-100 Install Manual

Testing the installation

Telnet connections to the SMTP port number

From the FortiMail unit to an SMTP server
To or through the FortiMail unit
FortiMail™ Secure Messaging Platform Version 4.0 Patch 1 Install Guide
Revision 2
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Note: Like verifying DNS connectivity and configuration from the FortiMail unit, you may
also be able to verify DNS connectivity and configuration from protected and external mail
servers using similar commands. This can be necessary if the devices are configured to
use different DNS servers. For details, see the documentation for those mail servers.
Instead of using an SMTP client to verify SMTP connections, you can manually establish
SMTP connections by using a Telnet client. Especially if your SMTP client or SMTP server
is unable to establish a connection, manually attempting the connection may provide you
with SMTP error codes or other insight into why the connection is failing.
Table 8: Some common SMTP error codes
SMTP error Description
code number
500 Syntax error, command unrecognized
501 Syntax error in parameters or arguments
502 Command not implemented (such as for ESMTP and other SMTP
protocol extensions that are not enabled/installed on the SMTP server)
503 Bad sequence of commands
If extended SMTP error codes have been installed and enabled on the target SMTP
server, a manual Telnet connection may enable you to view additional error descriptions.
For example, the enhanced error code 4.3.2 Please Try Again Later may notify
you that a temporary condition exists preventing delivery, such as greylisting or service
unavailability, and that the SMTP client should try delivery again later.
How you should establish the connection depends on the origin and destination of the
SMTP connection that you want to test, either:
• from the FortiMail unit to an SMTP server
• to or through the FortiMail unit
If you are not sure if the FortiMail unit can use SMTP to reach an SMTP server, you might
use the execute telnettest <fqdn_str>:<port_int> CLI command.
For example, to test SMTP connectivity with mail.example.com on the standard SMTP
port number, 25 (commands that you would type are highlighted in bold; responses from
the FortiMail unit are not bolded):
FortiMail-400 # execute telnettest mail.example.com:25
Connecting to remote host succeeded.
If you are not sure if a MUA can use SMTP to reach a FortiMail unit that is operating in
gateway mode or server mode, or not sure which SMTP commands the FortiMail unit has
been configured to accept, from the email user's computer or an external SMTP server,
you might open a command prompt and use the command line Telnet client.
For example, to send a test email message (commands that you would type are
highlighted in bold; responses from the FortiMail unit are not bolded):
$ telnet fortimail.example.com 25
Trying fortimail.example.com...
Connected to fortimail.example.com.
Escape character is '^]'.
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