PHP mail formatting issue - Why do CRLF header line endings break HTML email in Outlook?

Question

I\'m using the PHP native mail() function to send HTML emails and have a formatting problem in the users most common email client - Outlook 2007

Answer 1

The email is been interpreted as text/plain instead of intended html. The reason for this is that text/html is a multipart subtype thus requiring boundary declarations.

Your code is missing a the header boundary declaration:

$message  = get_HTML_email_with_valid_formatting();
$headers  = "MIME-Version: 1.0\r\n";
$headers .= "--$boundary\r\n"."Content-Type: text/html; charset=ISO-8859-1\r\n";
$headers .= "From: example.com \r\n";
$headers .= "Reply-To: donotreply@example.com\r\n";
mail('me@example.com', 'test', $message, $headers);

Check this wiki about MIME & Multipart Messages: http://en.wikipedia.org/wiki/MIME#Multipart_messages