Because I always forget this, here is the command line syntax for sending a test email through an SMTP mail server. Commands to enter at a prompt are in RED.
telnet mail.whateverdomain.com 25
Connected to whateverdomain.com.
Escape character is '^]'.
220-whateverdomain.com Smail-220.127.116.11 (#2 1998-Jul-16) ready at Mon, 27 Nov 2000 13: 34:55 -0600 (EST)
250 yourdomain.com Hello yourmachine.yourdomain.com (yourdomain.com from address 18.104.22.168).
250 email@example.com ... Sender Okay
250 'firstname.lastname@example.org' Recipient Okay.
354 Enter mail, end with "." on a line by itself
From: Meredith Foo
Subject: Test Message
This is only a test.
250 Mail accepted
221 whateverdomain.com closing connection
Don't forget that if your telnet session is hanging, the key combination of CTRL-] will exit you to the command prompt of telnet (Windows) or the shell prompt (Unix). If you're in Windows, simply type "quit" at the telnet command prompt in order to exit.
Expanding upon this simple test email, I've written some instructions on how to automate emails via shell script that some of you might find useful: