2007 Exchange server cannot see 2010 Exchange 2010 free/busy

Single forest multiple domains.   We are in co-existence with Exchange 2003, 2007, and 2010.  2003 and 2010 share a domain and 2007 is in its own domain.  
2010 users can see each other's free/busy as well as 2003 users seeing 2010 free/busy and 2010 sees 2003 free/busy.  However, a 2007 user cannot see a 2010 users free/busy, but the 2007 user can see the 2003 users free/busy.  I know that's extremely convoluted.
Internal EWS URL's are set to the respective external URL's (no FQDN's).  The bypassURL is showing the FQDN.    External EWS URL on 2007 is blank.  External URL on 2010 is the same as the internal.  
Thanks for any help.

Desktop>Get-WebServicesVirtualDirectory | Select name, *url* | fl

Name                 : EWS (Default Web Site)
InternalNLBBypassUrl : https://sv07tumail.xxxxx.local/ews/exchange.asmx
InternalUrl          : https://outlook.xxxxx.com/ews/exchange.asmx
ExternalUrl          :

Name                 : EWS (Default Web Site)
InternalNLBBypassUrl : https://sv18tumail.xxx.local/ews/exchange.asmx
InternalUrl          : https://test.xxx.com/EWS/Exchange.asmx
ExternalUrl          : https://test.xxx.com/EWS/Exchange.asmx
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Simon Butler (Sembee)ConsultantCommented:
With 2003 involved you need to have public folders on the other servers and replicate the system folders - including free/busy. Therefore the first thing I would do is check that is setup correctly.
Does the host name on the internal bypass URL appear on the SSL certificate on the server itself? Is the certificate trusted by the clients?


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bfpnaeechangeAuthor Commented:
Thanks for the comment.  The internal bypass URL is not on the SSL cert since it's a .local.  The system folders are being replicated from 2003 to all the Exchange servers.   However, the issue is strictly with Exchange 2007 users seeing Exchange 2010 free/busy.
bfpnaeechangeAuthor Commented:
SV07 is Exchange 2007 and SV18 is Exchange 2010 in the above example.
Simon Butler (Sembee)ConsultantCommented:
If the internal bypass URL is not on the SSL certificate, then Outlook is going to have problems connecting to it, because it cannot create the trust.
You either need to use a URL that is on the certificate, or stop using SSL for that URL.

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