There are a lot out there; but my favourite is been PHPMailer
I was always on the look for a decent php mail class with smtp auth and mime mail support. Then one day stumbled on this sourceforge project. There it was with other features too which I wished to have
- Can send emails with multiple TOs, CCs, BCCs and REPLY-TOs,
- Redundant SMTP servers, Multipart/alternative emails for mail clients that do not read HTML email,
- Support for 8bit, base64, binary, and quoted-printable encoding,
- Uses the same methods as the very popular AspEmail active server (COM) component,
- SMTP authentication,
- Word wrap,
- Address reset functions,
- HTML email,
- Tested on multiple SMTP servers: Sendmail, qmail, Postfix, Imail, Exchange, etc,
- Works on any platform,
- Flexible debugging,
- Custom mail headers,
- Multiple fs, string, and binary attachments (those from database, string, etc),
- Embedded image support