Using Classic Outlook on Windows for personal email, calendar, and contact management
Hi houman Alavehzadeh,
Thank you for posting on Microsoft Forum.According to your description, I understand that you want the move forward or backward between emails when opening email in a separate window.
From my understanding you might add these buttons from File > Options > Quick access toolbar > then Choose command from all commands > Add Previous item and Next Item then click OK, to get these buttons available, make sure Quick Access Toolbar is not hidden.
Looking forward to hearing from you.
Best Regards,
De Paul