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 ...