I demonstrated how to build a modular MIME mailer class in PHP 4; it was provided with the capacity to send messages in plain text, and to work with different types of file attachments. This class implements a private method, called "getMimeTypes()," which, as its name would suggest, comes in handy for determining the correct MIME type of a given file. [...] However, the logic implemented by this method is rather primitive and can definitely be improved.

They start with a review of the previous code (PHP4) and show how to get the correct mime type of the file based on the extension mapped to an array of types.