Testing SMTP host with telnet

1. Telnet to port 25 on the host:

  telnet smtp.yourdomain.com 25

You should see something like:

 Trying X.X.X.X...
 Connected to smtp.yourdomain.com.
 Escape character is '^]'.
 220 smtp.yourdomain.com ESMTP Sendmail 8.14.4/8.14.4; Mon, 16 May 2011 04:34:09 GMT

2. Respond with

 HELO somedomain.com

You should see something like:

 HELO somedomain.com.com
 250 smtp.yourdomain.com Hello somedomain.com [X.X.X.X], pleased to meet you

3. Tell it where the mail is from:

 MAIL FROM: me@somedomain.com

You should see something like:

 250 2.1.0 me@somedomain.com... Sender ok

4. Tell it who the recipient is:

 RCPT TO: somedude@somedomain.com

You should see:

 250 2.1.5 somedude@somedomain.com... Recipient ok

5. Compose the email:

 DATA
 SUBJECT: testing mail
 hello. this is a test.
 .

You should see:

 DATA
 354 Enter mail, end with "." on a line by itself
 SUBJECT: testing mail
 hello. this is a test.
 .
 250 2.0.0 r534bJIb013152 Message accepted for delivery