Hi @Sue
Thank you for posting your question in the Microsoft Q&A forum.
I've tried many methods, but I still haven't found a solution for you. I'm truly sorry for the inconvenience. There is no setting related to changing the default popup size in New Outlook. If you believe this change is essential, we kindly encourage you to submit your feedback to Microsoft through the Ideas · Community. User feedback can occasionally influence future updates and feature enhancements.
If you have any further questions or need additional assistance, please feel free to ask. If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
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