A nice Addon, thank ypu.
Some suggestions, right now it shows a blank sticky note by default, even for guests. That makes no sense to me and there should be an option to disable it.
If a message is read and dismissed by an user, the message should get deleted also in the database . The privacy of my members is very important to me and this additional option would be very useful. And as far as I can see, the user can't read all of his sent and received notes on a later time, so it makes no really sense to store the messages for longer than necessary.