Email account isn’t configured with D365 error

Last week I had an issue with the Dynamics 365 for Outlook App. I had connected outlook to my sandbox environment and now I needed to remove that configuration and connect it to the production environment instead. Note, I had done this many times before in this tenant.
After configuring the mailboxes in both instances, I opened Outlook and clicked the Dynamics 365 button to test the integration. An error message popped up that read:”We’re sorry. We can’t load this app because your email account isn’t configured with Dynamics 365 server-side sync for appointments, contacts and tasks.”

Let’s go through the configuration steps to change the instance outlook is connected to (the sandbox instance) to the production instance. The first thing I did was open my sandbox instance and change all of the synchronization settings in my mailbox (incoming email, outgoing email and Appointments, Contacts and Tasks) to none. I then navigated to my mailbox in the production environment (settings>email configuration>mailboxes) and set the incoming email, outgoing email and Appointments, Contacts and Tasks in the production environment to Server Side Synchronization or Email Router. After saving my changes I approved my email and tested and enabled the mailbox.

When you click “Test & Enable Mailbox” a screen pops up. Make sure you check the box that reads:”If this mailbox was previously configured to sync with another organization, checking this option will switch it to sync with this organization.”

After some troubleshooting I navigated to settings>Dynamics 365 App for Outlook and noticed my mailbox already showed as Added to Outlook and everything looked fine, but I was still getting the error.

I decided to click the “Add App for All Eligible Users” button, which re-runs the process of adding the the app to outlook. I waited until the status changed back to Added to Outlook. After this I tested it in Outlook and the Dynamics 365 App for Outlook was fully functioning again!