We have two domains with AD two-way trust and Exchange GAL synchronization done via Forefront identity Manager 2010. We have a problem with meeting room reservation, user from domain A is trying to book meeting room from domain B (there is a contact object in domain A for this meeting room from domain B). The problem is that such room is not sending response confirmation email to user and meeting room is visible as tentative. I already found https://social.technet.microsoft.com/Forums/exchange/en-US/298ee741-3293-438c-bd2d-edc33d1aa408/unable-to-book-meeting-rooms-from-trusted-forest-rooms-are-tentative?forum=exchange2010

and set "externally secured" option on receive connector in domain B (exchange 2010 server). This didn't resolve our issue. How to troubleshoot it? 

Domain A: one exchange 2013 server

Domain B: one exchange 2010 server (meeting rooms hosted in db on this server) and 3 exchange 2013 servers in DAG, prepared to migrate mailbox db from 2010 server

Here is a message header from normal email sent from domainA to domainB - I am wondering what IP scope (private IP address of exchange server from domainA: 192.168.128.235 or public IP address of ironport from domainA 62.xxx.xx.10) should be set for receiver connector in domainB

Received: from 312EX.domainB.com (172.16.64.143) by
 316EX.domainB.com (172.16.64.231) with Microsoft SMTP Server (TLS)
 id 15.0.995.29 via Mailbox Transport; Mon, 7 Sep 2015 09:32:17 +0200
Received: from 317EX.domainB.com (172.16.64.232) by
 312EX.domainB.com (172.16.64.143) with Microsoft SMTP Server (TLS)
 id 15.0.995.29; Mon, 7 Sep 2015 09:32:16 +0200
Received: from 231EX.domainB.com (172.16.64.60) by
 317EX.domainB.com (172.16.64.232) with Microsoft SMTP Server (TLS)
 id 15.0.995.29; Mon, 7 Sep 2015 09:32:16 +0200
Received: from ironport.domainB.com (172.16.65.16) by
 231EX.domainB.com (172.16.64.60) with Microsoft SMTP Server id
 14.3.158.1; Mon, 7 Sep 2015 09:32:15 +0200
X-IronPort-Anti-Spam-Filtered: true
X-IronPort-Anti-Spam-Result: A0BCBQCdPO1V/wpblD5IFhkBgjwhLAEiMWkGrV2JWod4GgUBBYcjPBABAQEBAQEBgQqEKgwhHEIBDyRsBwEEG4gnAwGkbKQPhUJwiV2DIAxBgTEFlVWORoQziFCIPINsJoFKAQsBgilxh0SBBQEBAQ
X-IPAS-Result: A0BCBQCdPO1V/wpblD5IFhkBgjwhLAEiMWkGrV2JWod4GgUBBYcjPBABAQEBAQEBgQqEKgwhHEIBDyRsBwEEG4gnAwGkbKQPhUJwiV2DIAxBgTEFlVWORoQziFCIPINsJoFKAQsBgilxh0SBBQEBAQ
X-IronPort-AV: E=Sophos;i="5.17,484,1437429600"; 
   d="scan'208,217";a="10003978"
Received: from eta.domainA.com ([62.xxx.xx.10])  by ironport.domainA.com
 with ESMTP; 07 Sep 2015 09:32:15 +0200
Received: from ETA.domainA.com (192.168.128.235) by ETA.domainA.com
 (192.168.128.235) with Microsoft SMTP Server (TLS) id 15.0.1076.9; Mon, 7 Sep
 2015 09:34:20 +0200
Received: from ETA.domainA.com ([::1]) by ETA.domainA.com ([::1]) with
 mapi id 15.00.1076.000; Mon, 7 Sep 2015 09:34:20 +0200
From: =?iso-8859-2?Q?Be=B3ko_Bart=B3omiej?= <Bartlomiej.Belko@domainA.com>
To: "'bart.test@domainB.com'" <bart.test@domainB.com>
Subject: zaproszenie 
Thread-Topic: zaproszenie 
Thread-Index: AdDpP5kMyMCMbPmnRx2vAgAzt6KVkQ==
Date: Mon, 7 Sep 2015 07:34:19 +0000
Message-ID: <2331fe7580224c0b861e4209065012d0@ETA.domainA.com>
Accept-Language: en-US, pl-PL
Content-Language: pl-PL
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-ms-exchange-transport-fromentityheader: Hosted
x-originating-ip: [192.168.128.194]
Content-Type: multipart/alternative;
	boundary="_000_2331fe7580224c0b861e4209065012d0ETAdomainAcom_"
MIME-Version: 1.0
Return-Path: Bartlomiej.Belko@domainA.com
X-MS-Exchange-Organization-MessageDirectionality: Incoming
X-MS-Exchange-Organization-Network-Message-Id: 89c905ae-9f54-4c63-2553-08d2b7567491
X-MS-Exchange-Organization-AVStamp-Enterprise: 1.0
X-MS-Exchange-Organization-AuthSource: 231EX.domainB.com
X-MS-Exchange-Organization-AuthAs: Anonymous

• Edited by bbelko 17 hours 33 minutes ago