Send email with attachment: Send an email attachment files

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