WordPress SMTP MU-Plugin with support for multisite network

README.md

WordPress SMTP MU-Plugin

Configure SMTP with constants or site options with support for multisite networks.

Usage

1. Just download or copy this file
2. Place it under wp-content/mu-plugins/smtp-emails.php
3. Done.

smtp-emails.php

<?php

/**
 * Plugin Name:     SMTP
 * Plugin URI:      https://gist.github.com/lightningspirit/bb51e110d92821b724ab53bf2e07cb87
 * Description:     Send emails through SMTP server
 * Author:          Move Your Digital, Inc.
 * Author URI:      https://moveyourdigital.com
 * Version:         0.3.2
 *
 * @package         Smtp_Emails
 */

/*
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

/**
 * Fires after PHPMailer is initialized.
 *
 * @since 0.2.0
 *
 * @param PHPMailer $phpmailer The PHPMailer instance (passed by reference).
 */
add_action('phpmailer_init', function ($phpmailer) {

  if (!is_object($phpmailer)) {
    $phpmailer = (object) $phpmailer;
  }
  
  if (defined('WP_DEBUG') && constant('WP_DEBUG')) {
    $phpmailer->SMTPDebug = 2;
  }

  $smtp_host = get_option('smtp_host') ?: constant('SMTP_HOST');

  if ($smtp_host) {
    $phpmailer->IsSMTP();
    $phpmailer->Host = $smtp_host;
  }

  $smtp_auth = get_option('smtp_auth') ?: constant('SMTP_AUTH');

  if ($smtp_auth) {
    $phpmailer->SMTPAuth = $smtp_auth;
  }

  $smtp_port = get_option('smtp_port') ?: constant('SMTP_PORT');

  if ($smtp_port) {
    $phpmailer->Port = $smtp_port;
  }

  $smtp_username = get_option('smtp_username') ?: constant('SMTP_USERNAME');

  if ($smtp_username) {
    $phpmailer->Username = $smtp_username;
  }

  $smtp_password = get_option('smtp_password') ?: constant('SMTP_PASSWORD');

  if ($smtp_password) {
    $phpmailer->Password = $smtp_password;
  }

  $smtp_secure = get_option('smtp_secure') ?: constant('SMTP_SECURE');

  if ($smtp_secure) {
    $phpmailer->SMTPSecure = $smtp_secure;
  }

  $smtp_email_from = get_option('smtp_from_email') ?: constant('SMTP_FROM');

  if ($smtp_email_from) {
    $phpmailer->From = $smtp_email_from;
  }

  $smtp_name_from = get_option('smtp_from_name') ?: constant('SMTP_NAME');

  if ($smtp_name_from) {
    $phpmailer->FromName = $smtp_name_from;
  }

  return $phpmailer;
});

/**
 * Filters the email address to send from.
 *
 * @since 0.1.0
 *
 * @param string $from_email Email address to send from.
 *
 * @uses wp_mail_from
 */
add_filter('wp_mail_from', function ($from_email) {
  $smtp_email_from = get_option('smtp_from_email') ?: constant('SMTP_FROM');

  if ($smtp_email_from) {
    return $smtp_email_from;
  }

  return $from_email;
});

/**
 * Filters the name to associate with the "from" email address.
 *
 * @since 0.1.0
 *
 * @param string $from_name Name associated with the "from" email address.
 *
 * @uses wp_mail_from_name
 */
add_filter('wp_mail_from_name', function ($from_name) {
  $smtp_name_from = get_option('smtp_from_name') ?: constant('SMTP_NAME');

  if ($smtp_name_from) {
    return $smtp_name_from;
  }

  return $from_name;
});

/**
 * In every visit to the site settings network, if the options
 * don't exist, create them so we can change in a per site basis.
 * 
 * @since 0.2.1
 */
add_action('admin_head', function () {
  if (! is_multisite()) return;
  if (get_current_screen()->id !== 'site-settings-network') return;

  $id = isset($_REQUEST['id']) ? (int) $_REQUEST['id'] : 0;

  switch_to_blog($id);

  if (null === get_option('smtp_host', null)) {
    $options = [
      'smtp_host', 'smtp_auth', 'smtp_port',
      'smtp_username', 'smtp_password', 'smtp_secure',
      'smtp_from_email', 'smtp_from_name',
    ];
    foreach ($options as $option) {
      add_option($option, '');
    }
  }

  restore_current_blog();
});