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:Mike Kleiman commented
I solved this by adding a custom field to the inbox layout. I named it pinned. right click on a column heading in the inbox home screen and select View Settings. select Other Settings. Select "allow in-cell" editing. Next, select columns and create a new column with yes/no. Add that column to the list of displayed columns. Select sort and change the default sort to your Pinned column descending and then received descending. Go back to the inbox and select teh pinned column and a Yes should appear and it should display at the top. This worked for me with outlook 2016. kinda crazy to have to do this to pin something...