Hi @Sandy Hays
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There is no relevant setting in Outlook to control which monitor it opens automatically.
Please kindly understand that many functions are not designed at present. Also, I was searching and noticed that a similar idea had been posted, and the Outlook team had marked the item as "We're reviewing this". I've added my poll there and I'll leave the link below so that you or others can also vote or comment there when they see this topic.
Feedback: https://feedbackportal.microsoft.com/feedback/idea/be56a154-76bd-ed11-83ff-000d3a1ab7d1.
According to my tests, you can set it in Windows to tick the primary monitor and then Outlook will open on the specific monitor.
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