Licensing
All the code here is covered by the PHPGuru license. A short summary is that for any sort of commercial use there is a small one-off licensing fee to pay, and for charity and educational use there is a reduced license fee.
You can read more about licensing here (where there's also a link to Google Checkout).
SMTP mail sending utility for PHP4
This is a utility for sending email for PHP4. I haven't worked on this for many years, and you may be interested in looking at my up-to-date PHP5 version.