Using PHPMailer in WordPress

WordPress uses PHPMailer for its wp_mail() function. A common problem is that PHPMailer is hidden behind this interface, so it's initially difficult for you, or plugins, to get at the underlying instance to change its parameters. For that reason, plugins often bundle their own copy of the PHPMailer package. This is generally a bad idea, as often it will not be kept up to date, and it's adding bloat to your Wordpress installation which already provides the package.

Fortunately WordPress provides a hook called phpmailer_init that allows you to get your hands on the internal PHPMailer instance and configure it. Then, when you call wp_mail, it will use the PHPMailer instance configured as you like.

To make this work, we ask WordPress (using add_action() to call a function we have defined when the phpmailer_init event happens. As the docs for this hook say, the function is passed an instance of PHPMailer, so we define the function to expect that.

The second parameter to add_action is a callable, which means there are multiple ways of providing a reference to code that will be run by this hook. The most straightforward is an anonymous function (which pollute your namespace with unnecessary functions that will never be called from anywhere else), but you can also provide a simple function name, class and method names in an array, and any of the other ways that PHP allows for callables. Note that the PHPMailer instance is passed by reference, so you don't need to return anything from this function.

add_action('phpmailer_init', function ($mailer){
  $mailer->isSMTP();
  $mailer->Host = "mail.example.com"; // your SMTP server
  $mailer->Port = 25;
  $mailer->SMTPDebug = 2;
  $mailer->CharSet  = "utf-8";
  //etc
});

Once you've set that up, calling wp_mail will work as usual, but using the configuration you set in this function instead of WordPress' own config.