$ telnet localhost 25
ehlo
mail from: a@b.com
rcpt to: me@mydomain.com
250 2.1.5 Ok
data
.
Subject: SMTP testing
Greetings from me
.
quit
221 2.0.0 Bye
Connection closed by foreign host.
$ telnet localhost 25
Trying 127.0.0.1...
telnet: Unable to connect to remote host: Connection refused
That means the server is not running, which you can confirm with Netstat:
# netstat -pant|grep :25
If it returns nothing, your SMTP server is not running
