I’m currently in the process of doing a test run of Microsoft Exchange 2007 to Exchange 2010 migration at work. Everything was going well. The following issue has had me stumped for most of the day, but I’ve just managed to resolve it so though would do a quick write-up if any other admins out there come accross the same thing.

Test Setup

Exchange 2007 (Mailbox Database, Hub Transport, CAS)
Exchange 2010 (Mailbox Database)
Exchange 2010 (CAS)
Windows 7 client with Outlook 2010 installed.

Desired outcome

Move all users and settings to Exchange 2010 and decommision the old Exchange 2007 server

Issue

I moved a couple of test users over to the Exchange 2010 mailbox, everything moved without a hitch, the user could log in Exchange 2010 webmail fine, however when opening outlook and going through the initial autodiscover steps the following error was shown:

“The connection to the Microsoft Exchange Server is unavailable. Outlook must be online or connected to complete this action.”

After much Google searching, head scratching, F’ing and cursing, I finally found where the problem lay….

Resolution

I checked on the 2010 CAS server to see if any logs where present in C:\Program Files\Microsoft\Exchange Server\V14\Logging\RPC Client Access, however nothing found. I checked the same location on the 2010 Mailbox server and sure enough the logs were there?

After looking through the RCA log with the most recent timestamp, the following errors were logged which basically said “The mailbox database is pointing to this server which doesn’t have the Client Access Server role installed on it”, meaning it was dropping logon connections as it didn’t know what to do with them.

I then carried out the following command in Exchange Management Shell

Get-MailboxDatabase | fl

The output of this showed that the RPCClientAccessServer property was indeed pointing at the Exchange 2010 database server. This issue was resolved by running the command of Set-MailboxDatabase -Identity "MailboxDatabaseID" -RPCClientAccessServer "CAS Server FQDN"

Logged back into the test client using Outlook 2010, this connected fine without problems and was now connecting to Exchange 2010 servers.