I was looking for a PHP SMTP email class and stumbled across this PHP email class by Manuel Lemos. PHPclasses.org is rapidly becoming my first port of call when I'm looking for a class to fill some general function in my code. Of all the scripting sites out there, and there are hundreds, this is possibly one of the few that I would recommend to people.
One of the reasons that I liked the script was the debugging feature that showed the server responses as they happened. I've been busy setting up firewalls, SMTP relays, and IIS (hate hate hate) so it was useful to be able to get debug info from my client software.
In any case the class worked flawlessly first time, it's free to use, and my client is happy.