when you set outlook mac to fullscreen mode, you will find it impossible to drag and drop an attachment from one mail to a new mail. let me explain it more clear: first, you click one item from the inbox pane, and the content of that mail will be shown properly in the read pane, and you can see the attachment there too; second, you want to reply this mail, so you click "reply" and you see another new window floating on the center of screen, now you want to add someone new to the mail loop to let them know what you say and THE ATTACHMENT! now, you will find you cannot drag the attachment from the original mail to this new mail window whatever you try switch windows. but if you exit from the fullscreen mode, you can easily drag an attachment from one mail to another new mail(new or reply or forward all is fine). I guess when it is under fullscreen mode, the focus has been set only into that floating window and lost any other responsive control even you try switch and drag. i wish you can think twice and find a better solution in this scenario, thanks a lot!