How to Create Dynamic WordPress Email Templates | http://www.ibenic.com/create-dynamic-wordpress-email-templates/

settings.php

<?php

function ibenic_email_template_settings() {
 	// Section 
 	add_settings_section(
		'email_templates_section',
		'Dynamic Email Templates',
		'ibenic_email_templates_section',
		'email-templates'
	);
 	
 	// Field 
 	add_settings_field(
		'email_template_user',
		'User Registered',
		'email_template_user_cb',
		'email-templates',
		'email_templates_section'
	);
 	
 	// Value under which we are saving the data by $_POST
 	register_setting( 'email-templates', 'email_template_user' );
 }
 
 add_action( 'admin_init', 'ibenic_email_template_settings' );

 function ibenic_email_templates_section() {
 	echo '';
 }

 function email_template_user_cb() {
 	$content = get_option('email_template_user');
 	wp_editor( $content, 'email_template_user' );
 }

settings_page.php

<?php

function ibenic_email_template_submenu() {
	add_submenu_page(
		'options-general.php',
	        'Email Templates',
	        'Email Templates',
	        'manage_options',
	        'email-templates',
	        'ibenic_email_template_submenu_cb' );
}
add_action( 'admin_menu', 'ibenic_email_template_submenu' );

function ibenic_email_template_submenu_cb() {
	?>
	<div class="wrap">
		<h2><?php _e( 'Email Templates', 'your_textdomain'); ?></h2>
		<form method="post" action="options.php">
			<?php 
			settings_fields( 'email-templates' );	//pass slug name of page, also referred
                        
			do_settings_sections( 'email-templates' ); 	//pass slug name of page
			submit_button();
			?>
		</form>
	</div>
	<?php
}

user_register.php

<?php

add_action( 'user_register', 'ibenic_email_template_on_register', 10, 1 );

function ibenic_email_template_on_register( $user_id ) {
    
    // Get User Object
    $user_info = get_userdata( $user_id );
    
    // Set Dynamic Data with placeholders and values
    $dynamicData = array(
    	'username' => $user_info->user_login,
    	'useremail' => $user_info->user_email);
    
    // Get Admin Email
    $emails = get_option( 'admin_email' );
    
    // Create Email Subject
    $subject = 'New User Registered:  ' . $user_info->user_login;
    
    // Name of our template (Settings Field)
    $template = 'email_template_user';
    
    // Sending email with our Class
    new WordPressEmail( $emails, $subject, $dynamicData, $template );

}

wpemail.php

<?php

 class WordPressEmail {

 	/**
 	 * Array or String of emails where to send
 	 * @var mixed
 	 */
 	protected $emails;

 	/**
 	 * Subject of email
 	 * @var string
 	 */
 	protected $title;

 	/**
 	 * Associative Array of dynamic data
 	 * @var array
 	 */
 	protected $dynamicData = array();

 	/**
 	 * Template used to send data
 	 * @var string
 	 */
 	protected $template;

 	/**
 	 * Prepared template with real data instead of placeholders
 	 * @var string
 	 */
 	protected $outputTemplate;
 	
 	// ...
 	
 }

wpemail2.php

<?php

class WordPressEmail {

  // ...
  
	public function __construct($emails, $title, $dynamicData, $template ){

		$this->emails = $emails;
		$this->title = $title;
		$this->dynamicData = $dynamicData;
		$this->template = $template;
		$this->prepareTemplate();
		$this->send();

	}
	
	// ...

 }

wpemail3.php

<?php

class WordPressEmail {

 	// ...

	private function prepareTemplate(){
		$template = $this->getTemplate();

		foreach ($this->dynamicData as $placeholder => $value) {

			// Ensure that the placeholder will be in uppercase
			$securePlaceholder = strtoupper( $placeholder );

			// Placeholder used in our template
			$preparedPlaceholder = "{{" . $securePlaceholder . "}}";

			// Template with real data
			$template = str_replace( $preparedPlaceholder, $value, $template );
		}

		$this->outputTemplate = $template;
	}

	private function getTemplate(){

	    	return get_option( $this->template );

	}

	private function send(){
        		
		wp_mail( $this->emails, $this->title, $this->outputTemplate );

	}
}