The following code can be used to send html emails using php:

/** define email fields **/
$email_text   = "<strong>Hello</b> <br /> This is an email in html format.";
$subject        = "Email subject";
$from_name  = "John Smith";
$from_email  = "john_smith@sender-email-address.com";
$to_email      = "abcde@receiver-email-address.com";

/** construct headers **/
$headers  = "From: $from_name <$from_email>\r\n";
$headers .= "Content-type: text/html\r\n";

/** send the email **/
if (mail($to_email, $subject, $email_text, $headers)) {
    echo "Html mail sent successfully.";        
} else {
    echo "Error";
}