Exchange 2010 - Cannot share any calendar anymore INTERNALLY, but it used to work just fine. Sharing works just fine if done outside LAN

Several months ago, this quick working but we don't know when or how. Exchange 2010 Internal LAN server with internal Active Directory with integrated DNS. Internal Domain name is etf.local. External domain name for email is @etff.org. Email works just fine both internally and externally with NO issues. But calendar sharing via Outlook 2010 will not work internally on the network. But if we take the same Outlook2010 [on a laptop for example] and go home and try to share the calendar or connect to a shared calendar it works just fine and dandy. It only will not work internally. Again, it used to work but somewhere in the past it quit and can't determine why. It is not calendar sharing permissions as it works just fine when it is done eternally.  When trying to share calendar internally, it just spins and spins trying to connect and errors out with "No connection", but of course email works just fine internally ... do the exact same thing EXTERNALLY and it connects and shares almost instantly. Any solutions would be most appreciated. Not an expert with Exchange so please be patient and kind with jargon and ambiguous statements - Thank you. :-)
comstratAsked:
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Jason CrawfordTransport NinjaCommented:
Can you clarify specifically how/what you're trying to share?  One guess could be the internal URLs for virtual directories.  Try this:

1. Open EMS and run these commands:

Get-WebServicesVirtualDirectory | fl InternalUrl,ExternalUrl
Get-OutlookAnywhere | fl Id,IISAuthenticationMethods,ClientAuthenticationMethod

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comstratAuthor Commented:
So, sorry. I didn't know anything was added here. I found the following and for the moment, appears to have resolved the issue of sharing calendars internally.

dns entry...

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