Hi @ReWinterhalter
Welcome to our forum!
Does the error occur recently on Outlook Desktop Client? To further confirm if the issue is more related to Outlook desktop client, if possible, please log in to the employee's web mail and do the same test to check if the issue persists.
And does the employee have any specific operation before the issue occurred?
Meanwhile, you may refer to the article and follow the instructions step by step:
In addition, i find a similar thread that many people find it useful, please feel free to refer to.
Hope it helps!
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our [documentation] to enable e-mail notifications if you want to receive the related email notification for this thread.