So you are using the new Office 2013 Preview and when you reply the window doesn’t pop-up, instead you get inline email editing, now this can be handy and sometimes for some who are used to the old way of doing things, annoying.
If you want to disable Inline Replies, follow the steps below.
Click on File > Options > Mail > Uncheck “use inline replies when replying or forwarding”
That’s it, click OK. The next time you reply or forward the window will pop-out.