WordPress mail from a local site, caught

1. Start Buggregator

Run the container. Port 8000 is the web UI, port 1025 is the SMTP server.

docker run --pull always \
  -p 127.0.0.1:8000:8000 \
  -p 127.0.0.1:1025:1025 \
  -p 127.0.0.1:9912:9912 \
  -p 127.0.0.1:9913:9913 \
  ghcr.io/buggregator/server:latest

2. Save the mu-plugin

Save this file in the mu-plugins directory, for example as smtp.php.

<?php
/**
 * Plugin Name: MU Buggregator SMTP
 */
if (! defined('WP_ENVIRONMENT_TYPE') || 'local' !== WP_ENVIRONMENT_TYPE) {
	return;
}
add_action( 'phpmailer_init', function( $phpmailer ) : void {
	$phpmailer->isSMTP();
    $phpmailer->Host = '127.0.0.1';
    $phpmailer->Port = 1025;
}  );

3. Check the environment type

The plugin returns early unless the WP_ENVIRONMENT_TYPE constant is defined and equals local. On staging and production it does nothing, so mail there is sent as before. If you set the type as an environment variable instead of a constant, check wp_get_environment_type() === 'local': WordPress reads both forms there (https://developer.wordpress.org/reference/functions/wp_get_environment_type/).

4. Use the service name in Docker

If WordPress runs in Docker Compose next to Buggregator, set $phpmailer->Host to the Buggregator service name, for example 'buggregator'.

5. Send an email and open it

Trigger an email from your local site, then open http://127.0.0.1:8000. You see the rendered HTML with a Desktop / Tablet / Mobile width switcher, the plain text version, the addresses, the attachments and the raw MIME source.

On phpmailer_init, the plugin tells PHPMailer to send over SMTP to Buggregator. Buggregator includes a fake SMTP server on port 1025 that stores each email and shows it in the UI instead of delivering it.