Indicate folders with new unread messages.
I have mail that sorts into many folders. Many of these contain messages I will never read and thus always have an unread message count. I would like to be able to easily see when these folders have new/recent messages.
One way to convey that would be to dim or change the color of the unread message count when the unread messages are "old".
There's a couple of options for deciding which unread messages are new and which are old. One simple approach would be to consider the unread messages to be new if they arrived since the last time the folder was viewed. This is my preferred approach.
The other approach would be to set a threshold, e.g. 48 hours. This doesn't work very well if you are away from email longer than the threshold. Also people would want it to be configurable, adding complexity.
Tony Stark commented
While the read and received receipts are really useful, it would be great if there could also be a way of receiving an alert if a read receipt has not been received within a time priod, thus indicating the recipient has not read the message yet. Thank you!