exchange server 2013

I have installed Active directory server 2012 with DNS and DHCP. Then I have installed Exchange server 2013 on the same server.

Now everything is working fine But i have issue with mailflow.

I can able to send and receive emails internal environment, and I can send an email internal to any external domain like gmail, yahoo etc.

My issue is that I can not able to receive emails from gmail, yahoo or any other domain from outside.

below is the detail of error message. Kindly suggest.



mx.kci-ster-dtc1.kci.net rejected your message to the following e-mail addresses:

2013Admin (2013Admin@VER2.District.local)


mx.kci-ster-dtc1.kci.net gave this error:
 < 2013Admin@contoso.com>: Recipient address rejected: User unknown in virtual mailbox table


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: mail.yahoo.com

2013Admin@da.com
 mx.kci-ster-dtc1.kci.net #550 5.1.1 <2013Admin@da.com>: Recipient address rejected: User unknown in virtual mailbox table ##

Original message headers:
Received: from mail.yahoo.com ([o0p9::0tf4:1m1j:r45t:45]) by
 mail.yahoo.com([o0p9::0tf4:1m1j:r45t:45]) with mapi id
 14.03.0174.001; Tue, 4 Mar 2014 04:34:19 -0600
From: abc <abc@yahoo.com>
To: 2013Admin <2013Admin@VER2.District.local>
Subject: RE: test 3.33
Thread-Topic: test 3.33
Thread-Index: AQHPN5UtQZ7u2yMLhE6vBDlyIBGYBZrQu2NH
Date: Tue, 4 Mar 2014 10:34:18 +0000
Message-ID: <0C565B911086D046B2F8034FED46006730A87696@mail.yahoo.com>
References: <0105f5dbc80b43518f9e9d7727fa5c10@VER2.District.local>
In-Reply-To: <0105f5dbc80b43518f9e9d7727fa5c10@VER2.District.local>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator:
x-originating-ip: [221.134.83.50]
Content-Type: multipart/alternative;
      boundary="_000_0C565B911086D046B2F8034FED46006730A87696BGHOEX01bgsndom_"
MIME-Version: 1.0

Kindly suggest......