
Hi Chris,
The error is just for one people? You can try to change another computer to test again.
You need try to test and enable the mailbox for server side synchronization. After re-running the Test and Enable process, install the app again.
Maybe you can try to add account in outlook to check the dynamics365 icon can appear or not?
If not, you can refer following link check other steps before the step or try to redeploy the app.
https://powerobjects.com/office-365-2/configuring-the-dynamics-365-app-for-outlook/
https://axforum.info/forums/showthread.php?t=77204
https://ramontebar.net/2017/11/23/fixing-dynamics-outlook-app-deployment-issues/
Regards,
Leah Ju
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