PHP: Sending Email (Text/HTML/Attachments)

So, you want to send automated email messages from your PHP application. This can be in direct response to a user's action, such as signing up for your site, or a recurring event at a set time, such as a monthly newsletter. Sometimes email contains file attachments, both plain text and HTML portions, and so on. To understand how to send each variation that may exist on an email, we will start with the simple example and move to the more complicated.