Advanced Email Techniques and MIME Handling

The Content-Type MIME e-mail header defines the boundary when sending MIME e-mails. The MIME-Version header specifies the version of the MIME protocol used, Content-Disposition specifies the presentation style of the content, and Content-Transfer-Encoding specifies the encoding of the content.

The fifth parameter of the mail function, $additional_parameters, is used to provide additional parameters to the sendmail application. It is typically only used in UNIX environments where sendmail is available, but can also be used in Windows/Novell environments with the sendmail_path configuration directive. The incorrect answers provided do not accurately reflect the correct usage of the $additional_parameters parameter.

This special MIME content type is used to define a segment which contains sub-segments representing multiple versions of the same content. For instance, a multipart/alternative segment may have two segments within it of types text/plain and text/html. It is then left to the e-mail client to choose the most appropriate format and display that to the user. As a general rule of thumb, it is always a good idea to put the easiest to read (i.e. plain text) versions first in the event that the mail is read from a non MIME-compatible e-mail client.