SMTP Check Port 25 with the Telnet Command

You can check your SMTP Server on SMTP port 25 with the following Telnet command:

Open a command line and type

telnet smtp-server.domain.com 25

If your server is online a connection will be established on port 25 (SMTP).

An Exchange Server answers with the following output:

220 mailserver.domain.com Microsoft ESMTP MAIL Service, Version: 5.0.2195.5329 ready at  Sat, 22 May 2006 08:34:14 +0200

When you type the ‘help’ command the available commands are listed:

214-This server supports the following commands:
214 HELO EHLO STARTTLS RCPT DATA RSET MAIL QUIT HELP AUTH TURN ATRN ETRN BDAT VRFY

Try the following to send an eMail from the command line:   

220 mailserver.domain.com Microsoft ESMTP MAIL Service, Version: 5.0.2195.5329 ready at  Sat, 22 May 2006 09:01:29 +0200
helo myserver.domain.com
250 mailserver.domain.com Hello [10.1.11.133]
mail from:<myname@mydomain.com>
250 2.1.0 myname@mydomain.com....Sender OK
rcpt to:<recipientname@mydomain.com>
250 2.1.5 recipientname@mydomain.com
data
354 Start mail input; end with <CRLF>.<CRLF>
subject: This is a test mail
to: recipientname@mydomain.com
This is the text of my test mail.
.
250 2.6.0 <exchange.domain.com> Queued mail for delivery
quit

If the mailserver returns a "syntax error" after the "mail from:" command, you've probably forgotten to put the mail address in brackets <>. 



The better way to Check Port 25 (free tool)

If you would like to check your SMTP Server at regular intervals, you can use the command line tool SLCheck. SLCheck connects to the SMTP Server and checks the answer. Batch files can be executed in dependance of the result, e.g. to send alarm notifications. Try the following command:

SLCheck -p 25 -a your-server.com -r "220"

220 is the normal answer from a SMTP Server.

All results are logged in a logfile. You can monitor your SMTP Server by running SLCheck as a scheduled task, e.g. once a minute.

SLCheck Homepage