If you haven’t yet had your fill of Microsoft betas, also known as Insider builds, and use the Outlook.com website, you can join the Outlook.com beta. This is an opt-in web experience, giving end-users the ability to try out “new product innovations” and share your experience with the Outlook.com product team. Microsoft will use the feedback to improve, refine, or discard the new features. When it's over, the best innovations will make it into Outlook.com.
If you want to be on the cutting edge (or are a glutton for punishment), click the ‘Try the beta’ toggle switch when it shows up in the top right corner of your Outlook.com Inbox. It’s rolling out in waves and if it's not there now, it will be within a few weeks. (You might want to try a different browser too, my account has it available in Chrome but not in Edge.) If you don’t like the new design, you can switch back to the regular web site at any time by sliding the toggle to the Off side.
Leave your suggestions or comments at the Outlook.com beta site on UserVoice.
BTW, I’m just kidding about being a glutton for punishment. The features they enable for beta users will be solid. it’s down to whether you want to see the new features ahead of everyone else or hate change and want to keep the old stuff around as long as possible.