Easy Mail: Compose and send HTML messages with attachments

This class can be used to compose and send HTML e-mail messages with optional attachment files.

The headers From, To, Subject and the Return-Path e-mail address can be defined as class variables.

The message can be composed and sent just by calling a single function which can be any of the variants to send plain text messages or HTML messages with or without an attachment file.

When sending HTML messages, the class includes a dummy plain text message part encapsulated withing a MIME multipart/alternative message part.