Hello Jennifer Lundy1,
Thank you for posting in Microsoft Community! We are happy to assist.
Based on your description, you want to open "Compose new email" in new tab. Kindly explain further if this is not the case.
Let's work together to have this challenge addressed ASAP.
Unfortunately there is no settings to configure to have this done automatically, however you can do it manually by following these steps:
after you click New Email, click the arrow in the far right side as shown below. This will open the new email in a new window as shown below


Please feel free to let me know if you have any other concern or if I get you wrong. Glad to assist you. We sincerely appreciate your patience and cooperation. Thanks for your precious time!
Note: Please understand that our initial reply may not always immediately resolve the issue. However, with your help and more detailed information, we can work together to find a solution.
Best regards
Community Moderator