inserting HTML into PHP generated emails

One of our clients wants to have a "clickable" URL for AOL members using the <A href= tag, we have a php3 file that we have put that code in as follows but it doesn't seem to be working, it simply throws the raw text to the email rather than the HTML, any idea what we are doing wrong? <HTML> <BODY> <?php $mailbody = "You have received an electronic mail sent to you by $from. \n\n Click on the following address to take you directly to your email: \n\n http://216.157.57.51/viewmessage.php3?id=$msgid \n\n If you are unable to click on the address above you may copy and paste that address into the address box in your browser and click go. \n\n Or please note the email number $msgid and enter it when prompted to do so at http://www.emailsmiling.com/viewmycard.htm>. \n\n If you wish to send an emailsmiling.com greeting just visit this site: http://www.emailsmiling.com \n\n Our colorful emails are easy and fun to create and they are absolutely free! \n\n Enjoy your email and don't just keep smiling, keep emailsmiling! \n\n Your friends at emailsmiling.com \n\n\n AOL Members:?> <a href='http://216.157.57.51/viewmessage.php3?id=$msgid'>Please Click Here to view your email</a><?php"; mail("$to_email", "emailsmiling.com electronic email", "$mailbody", "From: Emailsmiling@emailsmiling.com"); ?> </BODY> </HTML> Erik