The file is not an Outlook data file (.ost).вЂ™ I am able to access OWA and configure a profile on an Outlook client successfully, but when attempting to open Outlook, I get the error: IвЂ™m running into the following issue after introducing Exchange 2016 and cutting over the namespace: Our exchange environment is about as basic as it gets: 1 Exchange 2010 running Hub, CAS, MBX and all of our incoming mail is delivered from a third party spam filter appliance. InВ the Exchange Management Shell, run the following command to move the mailboxes to a database on your Exchange 2016 server.ДЇirst off, I just want to thank you for putting together these guides, they are absolutely amazing and extremely helpful. The mailboxes themselves are typically quite small and will move fairly quickly. Arbitration mailboxes are responsible for things like transport moderation and audit logging, and need to be hosted on the highest version of Exchange in the organization. The final task before any production services are cut over to Exchange 2016 is to move the arbitration mailboxes. You can follow the steps outlined in this article to modify the hosts file. To perform this test you can use a hosts file entry on a test workstation, to point that single clientвЂ™s connections to the Exchange 2016 server. To avoid an unexpected problem, itвЂ™s advisable to test the client access change before you modify the DNS record. If thereвЂ™s a problem, it will impact all of the users. If you change the DNS record for your client access namespace, all of your users will begin making connections for some Exchange services to the Exchange 2016 server. The cutover of client access namespaces to Exchange 2016 involves a DNS change. For example, Not Real University uses the user principal name (UPN) as the logon format, which matches the usersвЂ™ primary email addresses. If you have a different logon format requirement you should make those changes to the virtual directory settings now before you cut over any namespaces or move any mailboxes. The default OWA authentication settings for a newly installed Exchange 2016 server are:

The following command will display the Outlook Anywhere configuration for Exchange 2010 servers. For Exchange 2010 mailbox users, Outlook Anywhere authentication needs to be configured on the 2010 server to allow the proxied connections to work. When the client access namespaces are cut over to the Exchange 2016 server, Outlook Anywhere connections for Exchange 20 mailbox users will be proxied from the 2016 server to the 2013 or 2010 server.

Perform Outlook tests on the network including creating a new Outlook profile, scheduling a meeting and viewing free/busy information for attendees, accessing public folders, and sending/receiving internal and external email.

Review your server event logs for any unusual errors.

Verify that backups for the existing and new Exchange servers are running successfully.

Use the Remote Connectivity Analyzer to test external access such as Outlook Anywhere and ActiveSync.Run the Test-ExchangeServerHealth.ps1 script.If you start a migration, then notice the problems, troubleshooting is more complicated because you will be unsure whether the problem has been caused by the migration or not. The reason for performing a health check now is to determine if there are any existing problems that you might not already be aware of.

Health CheckДЇirst, itвЂ™s advisable to perform a general health check of the existing production environment. Before any services are cut over, thereвЂ™s some preparation tasks to perform. This stage is referred to as coexistence. The Exchange 2016 migration for Not Real University is getting to the stage where they can start cutting over client access and transport services to the Exchange 2016 Mailbox server.

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