A php tutorial/walkthrough that shows how to realize a useful feature like the one to send an url of your site via mail. http://www.cagedflame.com/index.php?name=sendthispage.php
This php tutorial shows you how to send password to members via e-mail address when they forgot their password. http://www.phpeasystep.com/workshopview.php?id=21
When users sign up to join your website you may want to verify their email address by sending confirmation link to their email address. http://www.phpeasystep.com/workshopview.php?id=24
You can apply this tutorial for your contact form on your sites. This tutorial shows you in 1 file with a normal contact information form. http://www.phpsimple.net/tutorials/form_to_email/
When you create an auto email sender program with mail() function. You can not to test it on your machine(localhost). http://www.phpsimple.net/tutorials/create_email_server/