What pattern does this use?

email.php

<?php
class Email implements EmailInterface
{
    /**
     * Email Handler
     *
     * @var     object
     * @since   1.0
     */
    protected $handler;

    /**
     * Constructor
     *
     * @param  EmailInterface $email
     *
     * @since  1.0
     */
    public function __construct(EmailInterface $email)
    {
        $this->handler = $email;
    }

    /**
     * Return parameter value or default
     *
     * @param   string $key
     * @param   string $default
     *
     * @return  mixed
     * @since   1.0
     */
    public function get($key, $default = null)
    {
        return $this->handler->get($key, $default);
    }

    /**
     * Set parameter value
     *
     * @param   string $key
     * @param   mixed  $value
     *
     * @return  $this
     * @since   1.0
     */
    public function set($key, $value = null)
    {
        $this->handler->set($key, $value);

        return $this;
    }

    /**
     * Send Email
     *
     * @return  mixed
     * @since   1.0
     */
    public function send()
    {
        $this->handler->send();

        return $this;
    }
}

class PhpMailer extends AbstractHandler implements EmailInterface
{
  // get, set, send methods that interact with phpMailer
}

class Swiftmailer extends AbstractHandler implements EmailInterface
{
  // get, set, send methods that interact with Swiftmailer
}

// To use


// 1. Instantiate an Email Handler.
$options                     = array();
$options['mailer_transport'] = 'mail';
$options['site_name']        = 'Sitename';

$class   = 'Molajo\\Email\\Swiftmailer';
$handler = new $class($options);

// 2. Instantiate the Email class, injecting it with the Handler.
$class         = 'Molajo\\Email';
$email = new $class($handler);

// 3. Set email parameters
$email->set('to', 'AmyStephen@gmail.com,Fname Lname');
$email->set('from', 'AmyStephen@gmail.com,Fname Lname');
$email->set('reply_to', 'AmyStephen@gmail.com,FName LName');
$email->set('cc', 'AmyStephen@gmail.com,FName LName');
$email->set('bcc', 'AmyStephen@gmail.com,FName LName');
$email->set('subject', 'Welcome to our Site');
$email->set('body', 'Stuff goes here');
$email->set('mailer_html_or_text', 'text');

// 4. Send Email.
$email->send();

Combination proxy (the email class proxies to the underlying handler instance) and adapter (specific handlers).

Thank you, @weierophinney