cannot send internal email to an account and get a bounce back every time

hi, I have a user who can't send an email to a user and gets the below bounce back.
I have updated the address book but get an exchange error. he is running outlook 2007 on exchange 2007. I have tried it in cached and non cached mode.

Delivery has failed to these recipients or distribution lists:
 
Richard Aylward
The recipient's e-mail address was not found in the recipient's e-mail system. Microsoft Exchange will not try to redeliver this message for you. Please check the e-mail address and try resending this message, or provide the following diagnostic text to your system administrator.
 
  _____  
Sent by Microsoft Exchange Server 2007




 
Diagnostic information for administrators:
 
Generating server: e2007.sub.mydomain.co.uk
 
IMCEAEX-_O=domain_OU=First+20administrative+20group_cn=Recipients_cn=ra@mydomain.co.uk
#550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found ##
 
Original message headers:
 
Received: from e2007.sub.mydomain.co.uk ([192.168.1.183]) by
 e2007.sub.mydomain.co.uk ([192.168.1.183]) with mapi; Wed, 21 Mar 2012
 16:43:45 +0000
Content-Type: application/ms-tnef; name="winmail.dat"
Content-Transfer-Encoding: binary
From: Andy Davis <akd@mydomain.co.uk>
To: Richard Aylward
        <IMCEAEX-_O=mydomain_OU=First+20administrative+20group_cn=Recipients_cn=ra@mydomain.co.uk>
Date: Wed, 21 Mar 2012 16:43:46 +0000
Subject: test
Thread-Topic: test
Thread-Index: Ac0HgciQ2d3fI0RwQEyvZ0G/DliaVw==
Message-ID: <BD04825CB9A73A45826F3E1AEB6D97988FCA853DD3@e2007.sub.mydomain.co.uk>
Accept-Language: en-US
Content-Language: en-US
X-MS-Has-Attach:
X-MS-TNEF-Correlator: <BD04825CB9A73A45826F3E1AEB6D97988FCA853DD3@e2007.sub.mydomain.co.uk>
MIME-Version: 1.0
X-ExProperty: MjE6VlRfQlNUUjpBbmR5IERhdmlz
X-ExProperty: MTM6VlRfVUk0OjA-
X-ExProperty: MTI6VlRfVUk0OjQ-
X-ExProperty: NzpWVF9VSTQ6MQ--
X-ExProperty: NjpWVF9VSTQ6MA--
X-ExProperty: NTpWVF9VSTQ6MQ--
X-ExProperty:
 NDpWVF9CU1RSOi9vPVJPVEFNQVQvb3U9Zmlyc3QgYWRtaW5pc3RyYXRpdmUgZ3JvdXAvY249UmVjaXBpZW50cy9jbj1ha2Q-
X-ExProperty:
 MzpWVF9CU1RSOkNOPUFuZHkgRGF2aXMsT1U9VXNlcnMsT1U9SHViZXIsREM9cm90YW1hdCxEQz1odWJlcixEQz1jbyxEQz11aw--
X-ExProperty: MjpWVF9CU1RSOmFrZEBodWJlci5jby51aw--
X-ExProperty: MTpWVF9VSTQ6MQ--
LVL 1
total123Asked:
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AITProsCommented:
Have you tried to select the users email address my manually browsing to the Global Address list - i.e. click 'To' in the send window and then choose the Global Address List for the Address Book.
abhishek1986Commented:
Try sending the message after deleting the favorites entries in the drop down list.
Also if possible, don't select the mail address from the list and give a complete address and then send it.
If you have not tried sending it from OWA, you can try and check to be sure.
RammesteinCommented:
Please add x500 address on the recipients mailbox.
This will solve it.
Known issue.

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total123Author Commented:
there's already an x400 entry, no option to add an x500.
none of the other users have x500 address in the email address tab.
total123Author Commented:
i've found this site and followed the instructions. I'll get the user to test it tomorrow
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