are you asking how Unity knows if a remote message store is available or not? The windows monitor component pings the Exchange message store services on the remote servers to see if they're up and running - if they aren't, it's noted in the table of message stores that it is not available and users attempting to log into those mailboxes on that mailstore will not be allowed to do so (this avoids "wedging" the MAPI thread with a long login time out).
the list of mailstores available on the network is pulled from AD, of course.
If that's not what you were asking, please clarify a bit what you're looking for.
When Unity tries to submit a MAPI message to Exchange it is forced authenticate and then resolve the message against a GC. This is the only time the UMR goes to a GC and it isn't optional. Since MAPI requires the client to access a GC we couldn't go to SQL if we wanted to. So if an Exchange server goes down none of that changes. Unity will still be forced to access a GC.
If should also be noted that in all release builds of code Unity does not monitor the MAPI GC for availability because until recently the Microsoft MAPI code did not allow us to dynamically move to a new GC. However, Microsoft as created a patch for MAPI and we have coded Unity so that in the 4.0(4) release we can accept a GC referral from our partner Exchange server if the patch is applied and the partner Exchange server has a GC to refer.
Are you getting this error “Installer User Interface Mode Not Supported. The installer cannot run in this UI mode. To specify the interface mode, use the -i command-line option, followed by the UI mode identifier. The value UI mode identifiers...
The below trick might come handy when you have to add a new node to a cluster but you don't have or is unsure of the security password for the publisher. This procedure has been around for ages.
1) Login into the CLI of the Publisher.