试图将HTML放入电子邮件但它不起作用?

        $body = "<p style=\"text-align:center;\"><img src=\"http://www.codefundamentals.com/images/logo.gif\" /></p><br /><p>CodeFundamentals.com has posted a new article titled: <a href=\"http://www.codefundamentals.com/blog/ " . $articleURL . "\">".$articleTitle."</a>.</p><br /><br />You are recieving this e-mail because you subscribed to our newsletter. To unsubscribe, please <a href=\"http://www.codefundamentals.com/unsubscribe.php\">click here</a> and fill out the form.</p>";

If I just do the <img> and then some basic text then it sends so I know the HTML is being accepted. Am I escaping characters wrong?