How to create a custom email plugin for Wordpress

07 Jun 2014

Last week, I suddenly stopped receiving email notifications for my openshift hosted blog. I came to know after some reading that commonly used cloud hosts such as openshift, aws, etc. are usually blacklisted by most email servers, hence its not a good idea to use them to send mails.

In any case, why should I depend on my hosting provider for email sending. Until now, I had never bothered about how mail sending worked in wordpress as it used to work out of the box. So last week, I pulled up my socks and decided to put my php IDE and debugger to some good work.

I decided to use my sendgrid account to send mails. All that`s needed now is calling the web service with the credentials they’ve provided. But how to integrate this with my wordpress blog?

Once I located where the mail sending functionality is there in wordpress code, adding a new method was a piece of cake!! Turns out that wordpress, by default, just executes the “mail” command which is usually just a symlink on unix boxes actually pointing to /usr/bin/sendmail or something. I found it in a pluggable function wp_mail(). (see /wp-includes/pluggable.php). I also came to know from the codex that pluggable functions can be easily overridden by plugins.

Now all I had to do was write a small plugin in the /wp-content/plugins/sendgrid/ folder and override this wp_mail() function with whatever I want.

Lo and behold! I started receiving notifications for all comments and contact forms filled, by just writing this one plugin. I found the process so simple and easy to integrate with wordpress that I couldn’t help sharing with you. Here are the two php snippets that you need to place in /wp-content/plugins/your-plugin-name/ and activate it. Wordpress will do the rest!

(First one is the main plugin php file that displays the plugin in your admin menu and overrides the wp_mail function. The second php file contains the actual custom function that sends email via sendgrid.)

wp-content/plugins/sendgrid/myplugin.php:

<?php /**
 * Plugin Name: Sendgrid Plugin
 * Plugin URI:  http://prahladyeri.github.io
 * Description: Mail sending using Sendgrid Web API
 * Version:     0.1
 * Author:      Prahlad Yeri
 * Author URI:  http://prahladyeri.github.io
 * License:     MIT
 */

//namespace MailDemo;
require_once('sendgrid.php');

add_action( 'init', 'plugin_init' );

/**
 * Plugin Name: Prahlad's mail
 * Description: Alternative way to send a mail
 */
if (!function_exists('wp_mail')) 
{
	function wp_mail($to, $subject, $message, $headers = '', $attachments = array())
	{
		$sto = '';
		if (is_array($to))
		{
			$sto = implode(',',$to);
		} else {
			$sto = $to;
		}
		sendgridmail('wpadmin@mywebsite.com', $sto, $subject, $message, $headers);
	}
}

function plugin_init()
{
}

wp-content/plugins/sendgrid/sendgrid.php:

<?php //wp-content/plugins/sendgrid/sendgrid.php
function sendgridmail($from, $to, $subject, $message, $headers) {        
$url = 'https://api.sendgrid.com/';
$user='your-sendgrid-username';   
$pass='your-sendgrid-password';       
	
$params = array(       
'api_user'  ?> $user,
		'api_key'   => $pass,
		'to'        => $to,
		'subject'   => $subject,
		'html'      => '',
		'text'      => $message,
		'from'      => $from,
	  );


	$request =  $url.'api/mail.send.json';

	// Generate curl request
	$session = curl_init($request);
	// Tell curl to use HTTP POST
	curl_setopt ($session, CURLOPT_POST, true);
	// Tell curl that this is the body of the POST
	curl_setopt ($session, CURLOPT_POSTFIELDS, $params);
	// Tell curl not to return headers, but do return the response
	curl_setopt($session, CURLOPT_HEADER, false);
	curl_setopt($session, CURLOPT_RETURNTRANSFER, true);

	print_r('obtaining the response');
	// obtain response
	$response = curl_exec($session);
	print_r('closing curl session');
	curl_close($session);
	
	// print everything out
	//print_r($response);
}

//only for testing:
/*$to      = 'prahladyeri@yahoo.com';
$subject = 'Testemail';
$message = 'It works!!';
echo 'To is: ' + $to;
#wp_mail($to, $subject, $message, array() );
sendgridmail($to, $subject, $message, array());
print_r('Just sent!');*/

References: