WooCommerce: Send a custom admin email when a new customer creates a new account.

customer_registration_email_alert.php

<?php
namespace Your\Custom\Namespace;

/**
 * Send a custom admin email when a new customer creates a new account.
 * @param  integer $user_id The ID of the user whose data should be retrieved.
 * @return [type]          [description]
 */

function customer_registration_email_alert( $user_id ) {
    $user    = get_userdata( $user_id );
    $first_name = null;
    $last_name = null;
    $role = $user->roles;
    $email   = $user->user_email;
    
    // Retrieve $_POST values from WC signup form
    // Note read details in the codex, but you can't rely on 'user_register' hook to retrieve first_name, last_name values.
    // Not all values are stored in database when this hook runs https://codex.wordpress.org/Plugin_API/Action_Reference/user_register
    if ( isset( $_POST['sr_firstname'] ) ) {
        $first_name = $_POST['sr_firstname'];
    }

    if ( isset( $_POST['sr_lastname'] ) ) {
        $last_name = $_POST['sr_lastname'];
    }

    $message = sprintf( __('Rejoice someone loves us! A new customer, %1$s %2$s, with the email %3$s has registered.', 'yournamespace' ), $first_name, $last_name, $email ) ;
   
    // If new account doesn't have the 'customer' role don't do anything.
    if( !in_array( 'customer', $role ) ) {
        return;
    }

    wp_mail( [ 'youremail@yourcompany.com','anothercompany@anothercompany.com' ], 'New Customer Registration', $message );

}
add_action( 'user_register', __NAMESPACE__ . 'customer_registration_email_alert' );