1 function shop_mail($to, $subject, $body)
2 {
3     $headers = "From: shop@example.com\r\n"
4             .= "Bcc: shop-sent@example.com\r\n";
5     mail($to, $subject, $body, $headers);
6 }

 1 <?php
 2 function shop_mail($to, $subject, $body, $shop = 'original') {
 3     switch ($shop) {
 4         case: 'subdomain':
 5             $from = 'shop@subdomain.example.com';
 6             $bcc  = 'shop-sent@subdomain.example.com';
 7             break;
 8         case: 'original':
 9         default:
10             $from = 'shop@example.com';
11             $bcc  = 'shop-sent@example.com';
12             break;
13     }
14 
15     $headers = "From: $from\r\n"
16             .= "Bcc: $bcc\r\n";
17     mail($to, $subject, $body, $headers);
18 }

 1 <?php
 2 class ShopMail
 3 {
 4     protected static $from = 'shop@example.com';
 5     protected static $bcc  = 'shop-sent@example.com';
 6 
 7     public static function send($to, $subject, $body) 
 8     {
 9         $headers = "From: " . static::$from . "\r\n"
10                 .= "Bcc: " . static::$bcc . "\r\n";
11         mail($to, $subject, $body, $headers);
12     }
13 }

1 <?php
2 class SubdomainMail extends ShopMail
3 {
4     protected static $from = 'shop@subdomain.example.com';
5     protected static $bcc  = 'shop-sent@subdomain.example.com';
6 }

1 <?php
2 define('MYENV', 'Subdomain');
3 
4 $mailer = MYENV . 'Mail::send';
5 call_user_func($mailer, $to, $subject, $body);

1 <?php
2 $config = new ArrayObject(array(), ArrayObject::ARRAY_AS_PROPS);
3 $config->env = "Subdomain';
4 
5 $mailer = $config->env . 'Mail::send';
6 call_user_func($mailer, $to, $subject, $body);

 1 <?php
 2 class Mailer
 3 {
 4     protected $from = 'shop@example.com';
 5     protected $bcc  = 'shop-sent@example.com';
 6     protected $contentType = 'text/plain';
 7 
 8     public function setFrom($from) { ... }
 9     public function setBcc($bcc) { ... }
10     public function setContentType($type) { ... }
11     public function send($to, $subject, $body)
12     {
13         $headers = "From: " . $this->from . "\r\n"
14                 .= "Bcc: " . $this->bcc . "\r\n"
15                 .= "Content-Type: " . $this->contentType . "\r\n";
16         mail($to, $subject, $body, $headers);
17     }
18 }

1 <?php
2 $mailer = new Mailer();
3 $mailer->setFrom($config->from)
4        ->setBcc($config->bcc)
5        ->setContentType('text/html');
6 $mailer->send($to, $subject, $body);

 1 <?php
 2 interface MailTransport
 3 {
 4     public function send($to, $subject, $body, $headers);
 5 }
 6 
 7 class MailHeaders extends ArrayObject
 8 {
 9     public function toString()
10     {
11         $headers = '';
12         foreach ($this as $header => $value) {
13             $headers .= $header . ': ' . $value . "\r\n";
14         }
15         return $headers;
16     }
17 }

 1 <?php
 2 class Mailer
 3 {
 4     protected $headers, $transport;
 5 
 6     public function setHeaders(MailHeaders $headers) {
 7         $this->headers = $headers;
 8         return $this;
 9     }
10 
11     public function getHeaders() {
12         return $this->headers;
13     }
14 
15     public function setTransport(MailTransport $transport) {
16         $this->transport = $transport;
17         return $this;
18     }
19 
20     /* ... */
21 }

 1 <?php
 2 class Mailer
 3 {
 4     protected $headers, $transport;
 5 
 6     public function \__construct(MailTransport $transport)
 7     {
 8         $this->setTransport($transport);
 9         $this->setHeaders(new MailHeaders());
10     }
11     public function send($to, $subject, $body)
12     {
13         $this->transport->send(
14             $to, $subject, $body, 
15             $this->headers->toString()
16         );
17     }
18 }

 1 <?php
 2 $mailer  = new Mailer(new SmtpTransport);
 3 $headers = new MailHeaders();
 4 // or $headers = $mailer->getHeaders();
 5 
 6 $headers['From']         = $config->from;
 7 $headers['Bcc']          = $config->bcc;
 8 $headers['Content-Type'] = 'text/html';
 9 $mailer->setHeaders($headers) // if instantiated separately
10        ->send($to, $subject, $body);

 1 <?php
 2 interface MailMessage
 3 {
 4     public function setTo($to);
 5     public function setSubject($subject);
 6     public function setBody($body);
 7     public function setHeaders(MailHeaders $headers);
 8 
 9     public function getTo();
10     public function getSubject();
11     public function getBody();
12     public function getHeaders();
13 }

 1 <?php
 2 interface MailHeaders
 3 {
 4     public function addHeader($header, $value);
 5     public function toString();
 6 }
 7 
 8 interface MailTransport
 9 {
10     public function send(MailMessage $message);
11 }

 1 <?php
 2 $message = new Message();
 3 $headers = new MessageHeaders();
 4 $headers->addHeader('From', $from)
 5         ->addHeader('Content-Type', 'text/html');
 6 $message->setTo($to)
 7         ->setSubject($subject)
 8         ->setBody($body)
 9         ->setHeaders($headers);
10 $transport = new SmtpTransport($config->transport);
11 $transport->send($message);