Rmail for PHP: How to send (HTML) email with attachments or HTML (MIME) emails with PHP

Formerly known as HTML Mime Mail

This is a PHP class which allows you to easily send email from your PHP scripts with attachments, HTML and embedded images.

Can send email with To,Cc, Bcc and Reply-To recipients
Can send email using the PHP mail() function, piping direct to Sendmail, Postfix, Exim and also via SMTP
Multipart email, with HTML and plain text for clients that don't support HTML
All encoding types supported: 7bit, 8bit, Base64 and Quoted-Printable
Easy to use API
Supports SMTP authentication
Works with Windows and Unix/Linux
Allows any headers to be set, including your own custom headers
Allows email priorities to be set
Allows the character set to be set for headers and the email body, giving non-English support
Add attachments or embed images from files, or PHP strings (eg for images/files held in databases)
Allows Return-Path to be set (for controlling where bounces are sent to)
Can return the resulting email instead of sending, to allow attaching of emails to other emails
Full API list
Five Comprehensive example scripts

For PHP5: Latest update is version 5, which works only with PHP5. Download it here. The class is very stable.