This weekend we had a scheduled power outage, so I shutdown all the servers at my site including the Exchange box. Today users from a remote location who open a couple shared mailboxes that are hosted from my site are unable to do so.
I have verified those users are in the correct security group, that security groups is listed with Full Access to these two mailboxes. Local users have no trouble opening the mailboxes in question.
I've checked the Event logs on both servers and am seeing nothing with regards to these two mailboxes, or the users trying to access them.
As a test I gave an Admin at the remote site Full Access to a totally different mailbox hosted here.. Outlook could not find that user. What's more, the test admin in the remote site CAN see the test mailbox listed in the GAL.