As you saw in the previous section, the only method of the "Mailer" class that was concretely implemented was its corresponding constructor. However, I'll show you the implementations of the other methods of this mailer class, so that you can understand these methods more easily.

Now, pay attention to the following code sample, which completes the definition of the "Mailer" class: Here it is:

class Mailer{

var $sender;

var $recipient;

var $subject;

var $headers=array();

function Mailer($sender,$recipient,$subject,$message){

// validate incoming parameters

if(!preg_match("/^.+@.+$/",$sender)){

trigger_error('Invalid value for email sender.',E_USER_ERROR);

}

if(!preg_match("/^.+@.+$/",$recipient)){

trigger_error('Invalid value for email recipient.',E_USER_ERROR);

}

if(!$subject||strlen($subject)>255){

trigger_error('Invalid length for email subject.',E_USER_ERROR);

}

if(!$message){

trigger_error('Invalid value for email message.',E_USER_ERROR);

}

$this->sender=$sender;

$this->recipient=$recipient;

$this->subject=$subject;

$this->message=$message;

// define some default MIME headers

$this->headers['MIME-Version']='1.0';

$this->headers['Content-Type']='multipart/mixed;boundary="MIME_BOUNDRY"';

$this->headers['From']='<'.$this->sender.'>';

$this->headers['Return-Path']='<'.$this->sender.'>';

$this->headers['Reply-To']=$this->sender;

$this->headers['X-Mailer']='PHP 4/5';

$this->headers['X-Sender']=$this->sender;

$this->headers['X-Priority']='3';

}

// create text part of the message

function buildTextPart(){

return "--MIME_BOUNDRYnContent-Type: text/plain; charset=iso-8859-1nContent-Transfer-Encoding: quoted-printablennn".$this->message."nn";

}

// create message MIME headers

function buildHeaders(){

foreach($this->headers as $name=>$value){

$headers[]=$name.': '.$value;

}

return implode("n",$headers)."nThis is a multi-part message in MIME format.n";

}

// add new MIME header

function addHeader($name,$value){

$this->headers[$name]=$value;

}

// send email

function send(){

$to=$this->recipient;

$subject=$this->subject;

$headers=$this->buildHeaders();

$message=$this->buildTextPart()."--MIME_BOUNDRY--n";

if(!mail($to,$subject,$message,$headers)){

trigger_error('Error sending email.',E_USER_ERROR);

}

return true;

}

}

At this moment, and after studying the recently-implemented methods of the above mailer class, you'll have to agree with me that things are definitely more interesting! As you can see, the class now has been provided with the capacity to incorporate any number of additional MIME headers via the "addHeader()" method to a particular email message. The "buildHeaders()" and "send()" methods have been concretely defined, turning the mailer class into a completely functional piece of code.

You should also notice how the respective header and body parts of the MIME-based message are internally assembled by the "send()" method, before sending the message in question to the specified recipient. For this specific case, I created a basic MIME boundary to delimit the different parts of the message, but you can use a different one as long as it fits the specifications of the MIME extension. Simple and understandable, isn't it?

Now everything looks good, since you hopefully learned how to build an expansible mailer class with PHP 4, which, for the moment, permits you to send MIME-compliant text messages with minor efforts.

However, I'm pretty sure that you're anxious to see how the previous "Mailer" class can be used in the context of a hands-on example. Therefore, in the last section of this tutorial, I'll build a short script that will demonstrate the functionality of the class.

To see how this practical example will be developed, please read the next few lines. I'll be there waiting for you.