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:Gladys commented
Adding a feature in outlook for messages where you can add a note to the message you are sending or receiving for follow-up, mark it visible or private.
This will allow you to find a message already sent, and have notes attached to it to see where you left off in the message, or tasks involved for the message.