In this new post to the SeeIT Consult blog they show you how to use the Google Mail STMP service to send emails directly from PHP - no local MTA required.

I use a local Apache/MySQL server on a laptop to do a lot of my development '" I don't need a full mail server just to send mail. Also SMTP servers on dynamically assigned IP addresses are so untrusted these days that you can be pretty much guaranteed that a decent spam filter will reject your email based on a RBL lookup. By using Google Mail's authenticated SMTP service you bypass this restriction.

Their solution uses the ssmtp tool instead - a simpler MTA that doesn't require near the setup of others. They show you how to adjust the config to handle the PHP emails, set up some users and configure PHP (the sendmail_path in the php.ini) to push the emails through it. Because of the configuration changes, it then knows enough to push those emails out to Gmail's SMTP.