emails/api/resources/routes/01_mailboxes.php

<?php
use ProVM\Common\Controller\Mailboxes;
use ProVM\Common\Controller\Messages;

$app->group('/mailboxes', function($app) {
    $app->post('/register[/]', [Mailboxes::class, 'register']);
    $app->delete('/unregister[/]', [Mailboxes::class, 'unregister']);
    $app->get('/registered[/]', [Mailboxes::class, 'registered']);
    $app->get('[/]', Mailboxes::class);
});

$app->group('/mailbox/{mailbox_id}', function($app) {
    $app->group('/messages', function($app) {
        $app->get('/grab[/]', [Messages::class, 'grab']);
        $app->get('/valid[/]', [Messages::class, 'valid']);
        $app->get('[/]', Messages::class);
    });
    $app->get('[/]', [Mailboxes::class, 'get']);
});