lbry.com/controller/action/MailActions.class.php

<?php

class MailActions extends Actions
{
  public static function executeSubscribe()
  {
    if (!Request::isPost())
    {
      return ['mail/subscribe'];
    }

    $nextUrl = Request::getPostParam('returnUrl', '/');
    if (!$nextUrl || $nextUrl[0] != '/' || !filter_var($nextUrl, FILTER_VALIDATE_URL))
    {
      $nextUrl = '/';
    }

    $email = Request::getPostParam('email');
    if (!$email || !filter_var($email, FILTER_VALIDATE_EMAIL))
    {
      Session::set(Session::KEY_LIST_SUB_ERROR,
        $email ? __('Please provide a valid email address.') : __('Please provide an email address.'));

      return Controller::redirect(Request::getRelativeUri());
    }

    $tag = Request::getPostParam('tag');

    $response = LBRY::subscribe($email, $tag);
    if ($response['error'])
    {
      return ['mail/subscribe', ['error' => $response['error']]];
    }

    return ['mail/subscribe', ['subscribeSuccess' => true, 'nextUrl' => $nextUrl]];
  }

  public static function executeSubscribed()
  {
    return ['mail/subscribe', ['confirmSuccess' => true, 'learnFooter' => true]];
  }


  public static function prepareSubscribeFormPartial(array $vars)
  {
    $vars += ['btnClass' => 'btn-primary', 'returnUrl' => Request::getRelativeUri()];

    $vars['error'] = Session::get(Session::KEY_LIST_SUB_ERROR);
    Session::unsetKey(Session::KEY_LIST_SUB_ERROR);

    return $vars;
  }

  public static function executeUnsubscribe(string $email)
  {
    $decodedEmail = Encoding::base64DecodeUrlsafe(urldecode($email));
    if (!$decodedEmail)
    {
      return ['mail/unsubscribe', ['error' => 'Invalid unsubscribe link']];
    }

    $response = LBRY::unsubscribe($decodedEmail);
    return ['mail/unsubscribe', ['error' => $response['error']]];
  }
}