Calendar error message

Hi All,

I have one Exchange Server 2010, which I host about Six domain names and normally I create email accounts from those domains.

one of our users try to send an invitation from our company calendar to the other domain calendar but she is not able to reach the other calendar with the different domain. She gets this error message:

contact your helpdesk.
Nicoxxx xxxxx
The e-mail address you entered couldn't be found. Please check the recipient's e-mail address and try to resend the message. If the problem continues, please contact your helpdesk.


Diagnostic information for administrators:
Generating server: Rxxxx2.intxxxn.rxxxxxxxx.xx
IMCEAEX-_O=NT5_ou=00000000000000000000000000000000_cn=569ADBC6A2B2FC44BD8F31523246AD02@intexxxxx.xxxxxxx.xxx
#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##
IMCEAEX-_O=NT5_ou=00000000000000000000000000000000_cn=30195C19CE483B47A35489851826BA8B@inxxxxx.xx.xx.x.xxx
#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##
Original message headers:
Received: from RTRxxxV02.intern.rccccccc.ch ([192.168xxx0.cc2]) by
 rtsrxv02.ixxxern.risixxxxx.xxh ([192.1xxxxx80.142]) with mapi id 14.03.xxxx9.002;
 Tue, 14 Nov 2017 10:11:14 +0100
Content-Type: application/ms-tnef; name="winmail.dat"
Content-Transfer-Encoding: binary
From: Rixxx  sssss   Calendar <rtcccccccc>
To: Axxxxxxxxxxxxxx...
        <IMCEAEX-_O=NT5_ou=00000000000000000000000000000000_cn=569ADBC6A2B2FC44BD8F31523246AD02@intern.risxxxxxx>,
        <Hxxxxxyk@rixxe.ch>, "'xxxxxxt@gmail.com'"
        <nxxxxxxxt@gmail.com>, Nicxxxxx xxxxxhat
        <IMCEAEX-_O=NT5_ou=00000000000000000000000000000000_cn=30195C19CE483B47A35489851826BA8B@intern.risingtide.ch>
CC: "'adxxxxxxk@gmail.com'" <adxxxxxxxxx@gmail.com>
Subject: Rxxxxxxx
Thread-Topic: Rxxxxxxxx
Thread-Index: AdM3cGWUdNPvuXn8TJGM7bdrDBZQ1AluB8hQ
Date: Tue, 14 Nov 2017 10:11:13 +0100
Message-ID: <8EA3544D4B76254F8C86906A7BD74D2656544F@rtsrv02.intern.risingtide.ch>
Accept-Language: en-US, de-CH
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator: <8EA3544D4B76254F8C86906A7BD74D2656544F@rxxxxx.intern.rixxxxx.ch>
MIME-Version: 1.0
X-Originating-IP: [192.168xxx0.146]