Name of custom contact not being displayed

Our exchange 2010 system has a large number of custom contacts for the self employed agents we work with.
Our mail clients (exchange 2010 and owa) used to display the name of the custom contact in the from field of a received email but its now displaying the email address or the from name the sender has configured.
When we send an email names/email addresses get resolved and show the name from the custom contact as expected so the Global Address List is fine.
For example;
James Smith sends an email from
we have a custom contact with an external email address of  james.smith@madeupaddress.ext and display name of Agent Smith

What should show in outlook is that the email is from Agent smith but what we see is James Smith.

So What changed?
Last week we started the process of finally decommissioning our exchange 2003 server. All the mailboxes moved a long time ago but we completed the steps in the link below of converting all the objects to 2010 and some part of that seems to have caused this issue.
Any thought?
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In Outlook if your type in the address for an external contact do it resolve to the correct display name? Have you tried using simple display named as discussed in the following article.
Hillarys-ICTAuthor Commented:
If the address is typed in for sending it resolves correctly.
We have tried using SND but not had any affect.
We think it maybe something with the external connector as per here:
Will try that.

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The article you posted is very interested .... Do you have a test environment you could try this in first?
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Hillarys-ICTAuthor Commented:
sadly not so its going to require some careful planning to implement.
I would suggest at least downloading VirtualBox and creating a Windows 2008 vm running Exchange just so you can walk through the process first just to be safe.. ;-)
Hillarys-ICTAuthor Commented:
We've made this change and it has resolved the issue.
We managed to test it first by pointing one domain we own and use for testing to the the server not currently acting as the default smtp receiver.
Hillarys-ICTAuthor Commented:
Solution found by further research by team members.
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