E-mail Send/Receive Issues

I am VERY new to exchange and just took over the management of this exchange server.  The users are complaining that some of the messages that they are sending are coming back and that some of the messages that people are sending them are not getting received.  Below is an example of one such error.  Also, I am getting certificate errors on certain web sites (they have multiple domains) and also when attempting to get mail on a smart phone.  I am kind of at al loos and not sure where to even start to troubleshoot this...HELP!!!

Delivery has failed to these recipients or distribution lists:
 
jabitante@bda.cpa.com
A problem occurred during the delivery of this message. Microsoft Exchange will not try to redeliver this message for you. Please try resending this message later, or provide the following diagnostic text to your system administrator.
 
  _____  
Sent by Microsoft Exchange Server 2007





 
Diagnostic information for administrators:
 
Generating server: SRVEXCVRBB.vrbusinessbrokers.com
 
jabitante@bda.cpa.com
#554 5.4.4 SMTPSEND.DNS.NonExistentDomain; nonexistent domain ##
 
Original message headers:
 
Received: from SRVEXCVRBB.vrbusinessbrokers.com ([::1]) by
 SRVEXCVRBB.vrbusinessbrokers.com ([::1]) with mapi; Thu, 8 Mar 2012 12:57:45
 -0500
From: JoAnn Lombardi <Jlombardi@vrbusinessbrokers.com>
To: "jabitante@bda.cpa.com" <jabitante@bda.cpa.com>
CC: JoAnn Lombardi <Jlombardi@vrbusinessbrokers.com>
Date: Thu, 8 Mar 2012 12:57:43 -0500
Subject: Forms to be signed.
Thread-Topic: Forms to be signed.
Thread-Index: Acz9VPXgmWhDzpRbRs24Xm+vAmNTFQ==
Message-ID: <BB59B06BAAD77646A70248518AB13D4C52500BCA38@SRVEXCVRBB.vrbusinessbrokers.com>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach: yes
X-MS-TNEF-Correlator:
acceptlanguage: en-US
Content-Type: multipart/mixed;
        boundary="_006_BB59B06BAAD77646A70248518AB13D4C52500BCA38SRVEXCVRBBvrb_"
MIME-Version: 1.0