Hello everyone and thank you for taking the time to request this feature. As part of our investigation on adding this capability, we ask that you please help us gather additional information on how you use Pin. This helps us to prioritize and design the feature to be exactly what you need to get more done!
Please use the below link to access a short survey about Pin:Garrett Anderson commented
I exclusively use the web based outlook.com application through internet explorer because of this one reason. Once the ability to pin/stick emails to the top of my inbox in outlook 2016 (and to synchronize online with the web based app) then I will jump in and start using Outlook 2016.
I want to be able to flag emails and pin them to the top without any extra sorting. Just like I can online. Online I can flag and email, I can pin an email to the top, and I can do both. Very effective in prioritizing my work.