I think it may be beneficial if you could have a way of messaging your friends when they're offline and you have something you want to tell them. There could be a mailbox in towns where you can go to read these messages, or maybe one in the UI or both.
Just a heads up though, there used to be a sticky thread in this forum that got a lot of attention and support. Plus it was acknowledged by Jmods at the time as a good idea that might not be possible and they’ll look into it.
The threads gone now, it’s been like 7+ years and still no mailbox, so I can’t see it happening as much as I’d like it to.Support
This is a really cool suggestion simply due to the amount of people who. Are online and whilst friends are offline, maybe you have an item for them or something else and can never reach them (due to work/life, time-zones etc. ) I would support seeing something like this maybe as the OP stated with a mailbox or perhaps with Postie Pete running about could interact with him and see if he has any mail for you?Khajiit always has wares, even if its not what you are seeking