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:Jonas Floyd commented
On the web outlook the "Pin" feather is very helpful to keep things that are important in clear view. it would be nice to have the same feature on the desktop app as well.