What is the best PHP html mail script class?: Send this mail every 15 days

This class can add scheduled jobs to a crontab file.

It can add a given task to a cron file tasks to be executed at time intervals specified in minutes, hours, days, months or week days.

The class executes the crontab program to read the specified cron job file and add it to the current user list of crontab entries.

Class that may be used to compose and send e-mail messages.

It features:

- User definable headers and body parts.
- MIME encoding of text and HTML body parts with user defined character encoding using quoted-printable.
- Addition of file parts (attachments) with automatic content type detection.
- Forwarding of messages received from somebody else as intact attachments
- Support for multipart/related messages (eg. HTML messages with embedded images, stylesheets, frames, etc..)
- Support for multipart/alternative messages (eg. text and HTML versions in the same message).
- Encoding of message headers with user defined character encoding using q-encoding.
- Definition of the error delivery address setting the Return-Path header calling sendmail program directly.
- Several sub-classes for sending messages by different methods: PHP mail() function, sendmail, qmail, SMTP (with support for authentication and direct delivery mode), maildrop in Microsoft IIS or Exchange Pickup folder.
- Wrappers that emulate the mail() function using the SMTP, sendmail and qmail delivery sub-classes.
- Support for sending personalized bulk mail by replacing the contents of the message parts that differ for each recipient.
- HTML and plain text message parts can be composed using template engines. An example that works with Smarty template engine is provided.
- Retrieving the composed message data or size without sending the message