On-site users cannot authenticate to Exchange server after power-shell changes; OWA works fine?

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We have been having a ton of certificate errors, due to our internal domain being "domain.local", and only having a single Exchange server with a wildcard cert "*.domain.local". To ensure that all Outlook users would connect directly to the external address (which had the proper certificate), I changed all of the internal/external settings in these instructions (http://exchangeserverpro.com/avoiding-exchange-2013-server-names-ssl-certificates/) to https://external.domain.com/_____.

Tested it on a few machines, no problems. The next day (today), getting 50% of users internally reporting that they cannot connect - keeps popping up user/pass window... Try to authenticate (domain\user and applicable password), but only get this error: "The connection to Microsoft Exchange is unavailable.  Outlook must be online or connected to complete this action." So far, no issue configuring externally, and the "Remote Connectivity Analyzer" shows no issues in any category.

OWA works fine, and as I mentioned, about 50% of users work normally after reboot. Stumped - can anyone help?
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Most Valuable Expert 2014

Commented:
Does the external name resolve internally?
If you run an Autodiscover test, do the correct host names come back?

Simon.
Senior Systems Admin
Top Expert 2010
Commented:
More than likely the autodiscover settings are cached with the old name of autodiscover.domain.local, so computers are getting screwed up. Try running a repair on the Outlook profile for a user who has the issue to see if that fixes the problem. If it doesn't, remove any autodiscover.domain.local entries in DNS, Then create a SRV record in the domain.local DNS zone for the _autodiscover service that points clients to the autodiscover.domain.com address. http://acbrownit.wordpress.com/2012/12/20/internal-dns-and-exchange-autodiscover/ has info near the bottom on configuring a SRV record.

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