$to.= $arg['email']. ","; // note the comma//$to .= "kelly@example.com";/* subject */$subject = "Registration Complete Thankyou";/* message */$message = '<html><head><title>Registration</title></head><body><table width="84%" border="0" cellspacing="0" cellpadding="0" align="center"> <tr> <td width="300" height="172"><img src="images/logo.jpg" alt="lunchwanted.com" width="303" height="172" /></td> <td width="418" height="172"><img src="images/logo-1.jpg" width="330" height="172" /></td> </tr> </table><table width="84%" height="150" border="0" cellpadding="0" cellspacing="0" align="center"> <tr><td height="15">Registration Complete- Thank you Mail</td></tr> <tr><td valign="top">______________________________</td></tr> <tr><td>Dear Mr.'.$arg['fname'].'</td></tr><tr><td>Thank you for Registering at www.yourdomain.com</td></tr><tr><td>Your login details are given below.</td></tr><tr><td>Email Address : '.$arg['email'].'</td></tr><tr><td>Password : '.$arg['pass'].'</td></tr><tr><td>Please Click the following link to complete your registration process</td></tr><tr><td><a href="http://yourdomain.com/confirm.php?email='.$arg['email'].'">Activate your account</a></td></tr><tr><td>This is an automated email, so please do not reply to this.</td></tr><tr><td>Thank you.</td></tr><tr><td>Regards.</td></tr><tr><td></td></tr></table></body></html>';/* To send HTML mail, you can set the Content-type header. */$headers = "MIME-Version: 1.0\r\n";$headers .= "Content-type: text/html; charset=iso-8859-1\r\n";/* additional headers */$headers .= "To:".$arg['email']."\r\n";$headers .= "From: $mailvariable\r\n";/* and now mail it */mail($to, $subject, $message, $headers);Please try this above coding we are doing like that it will working properly