I’ve been using this more and more and have finally memorized most (if not all) of it. But this is for those of us who don’t really like to remember useless information.

Start -> Run -> CMD
telnet
open mail.mailserver.tld 25
At this point the server should respond with a 220 mail.mailserver.tld ESMTP Mail Service.
ehlo test.com
The server then should respond with 250 mail.mailserver.tld along with all the supported features of the mail server
mail from:tester@test.com
250 Sender OK
rcpt to: admin@test.com
At this point, the server should say 554 Relay access denied. This means your server is not an open relay.
rcpt to: actualemailaddress@mailserver.tld
250 Recipient OK
data
354 Start Mail input; end with CRLF.CRLF
subject: subjecthere
You’ll have to hit enter twice after the subject, then go on and type the body.
body here.
Note the . at the end – you’ll have to type a return and another . to finish.
Then there should be a server response 250 Queued mail for delivery. You can quit now.
quit