Telnet port 25 / Telnet SMTP commands / Check SMTP Port  |  22-Apr-2024

SMTP check port 25 with the Telnet command

You can check your SMTP Server on SMTP port 25 with the following Telnet commands. Open a command line and type: 

telnet smtp-server.domain.com 25

You can also do this with PuTTY. Check the "Telnet" radio button and type 25 instead of 23 in the "Port" textbox.

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 ready at Wed, 20 Mar 2019 20:20:59 +0100

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

 

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

helo myserver.domain.com # if nothing happens, repeat this
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 Recipient OK

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

In newer Exchange versions the brackets are obsolete. 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 SMTP port 25 (free command line tool, no installation required)

You can check TCP port 25 (and other ports) with the TCP port check command line tool (www.portcheck-tool.com). It can be used like the Ping command:

PortCheck.exe MyServer 25

or continuous

PortCheck.exe -t MyServer 25

The result looks like this:

C:\Users\admin>portcheck -t smtp.office365.com 25 smtp.office365.com - Port 25 - OPEN - 30ms smtp.office365.com - Port 25 - OPEN - 34ms smtp.office365.com - Port 25 - OPEN - 40ms smtp.office365.com - Port 25 - OPEN - 47ms smtp.office365.com - Port 25 - OPEN - 30ms smtp.office365.com - Port 25 - closed smtp.office365.com - Port 25 - closed smtp.office365.com - Port 25 - closed smtp.office365.com - Port 25 - closed smtp.office365.com - Port 25 - OPEN - 30ms smtp.office365.com - Port 25 - OPEN - 29ms smtp.office365.com - Port 25 - OPEN - 41ms smtp.office365.com - Port 25 - OPEN - 33ms smtp.office365.com - Port 25 - OPEN - 38ms smtp.office365.com - Port 25 - OPEN - 32ms smtp.office365.com - Port 25 - OPEN - 34ms smtp.office365.com - Port 25 - OPEN - 30ms

The PortCheck tool is also part of the PingTool software, which is also freeware. A ping tool with TCP portcheck, but also a Wake On Lan tool Windows 11.

...or use PingTool - the graphical Port Check Tool

Ping Tool is more than just another ping tool: It's also a graphical Port Check Tool an a Wake on Lan tool for IT professionals. And it's free!

Have a look at the PingTool video on YouTube:

Often used TCP ports:

TCP Port 21 - FTP
TCP Port 22 - SSH
TCP Port 23 - Telnet
TCP Port 25 - SMTP --> article TCP Port Check SMTP 25
TCP Port 80 - HTTP
TCP Port 110 - POP3
TCP Port 135 - DCE / WMI
TCP Port 139 - NetBIOS
TCP Port 143 - IMAP4
TCP Port 443 - HTTPS
TCP Port 445 - SMB
TCP Port 1433 - MS SQL
TCP Port 1494 - ICA (Citrix)
TCP Port 1521 - Oracle
TCP Port 3389 - RDP
TCP Port 5060 - SIP
TCP Port 8080 - HTTP Alternative
TCP Port 8443 - HTTPS Alternative