--PHP-alt-
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Hello World!!!
This is simple text email message.
--PHP-alt-
Content-Type: text/html; charset="iso-8859-1"
Content-Transfer-Encoding: 7bit
Hello World!
This is something with HTML formatting.
--PHP-alt---