MailboxTable::getOwnerId

static function getOwnerId($mailboxId): int
{
	$mailbox = self::getList([
		'select' => [
			'USER_ID',
		],
		'filter' => [
			'=ID' => $mailboxId,
		],
		'limit' => 1,
	])->fetch();

	if (isset($mailbox['USER_ID']))
	{
		return (int) $mailbox['USER_ID'];
	}

	return 0;
}