CIntranetUtils::IsExternalMailAvailable

static function IsExternalMailAvailable()
{
	global $USER;

	if (!is_object($USER) || !$USER->IsAuthorized())
		return false;

	if (!IsModuleInstalled('mail'))
		return false;

	if (COption::GetOptionString('intranet', 'allow_external_mail', 'Y') != 'Y')
		return false;

	if (CModule::IncludeModule('extranet') && CExtranet::IsExtranetSite())
		return false;

	if (isset(BitrixMainApplication::getInstance()->getKernelSession()['aExtranetUser_'.$USER->GetID()][SITE_ID]))
	{
		if (!BitrixMainApplication::getInstance()->getKernelSession()['aExtranetUser_'.$USER->GetID()][SITE_ID])
			return false;
	}
	else if (CModule::IncludeModule('extranet') && !CExtranet::IsIntranetUser())
		return false;

	if (!IsModuleInstalled('dav'))
		return true;

	if (COption::GetOptionString('dav', 'exchange_server', '') == '')
		return true;

	if (COption::GetOptionString('dav', 'agent_mail', 'N') != 'Y')
		return true;

	if (COption::GetOptionString('dav', 'exchange_use_login', 'Y') == 'Y')
		return false;

	if (!CUserOptions::GetOption('global', 'davex_mailbox'))
	{
		$arUser = CUser::GetList(
			'ID', 'ASC',
			array('ID_EQUAL_EXACT' => $USER->GetID()),
			array('SELECT' => array('UF_BXDAVEX_MAILBOX'), 'FIELDS' => array('ID'))
		)->Fetch();

		CUserOptions::SetOption('global', 'davex_mailbox', empty($arUser['UF_BXDAVEX_MAILBOX']) ? 'N' : 'Y');
	}

	if (CUserOptions::GetOption('global', 'davex_mailbox') == 'Y')
		return false;

	return true;
}