i sometimes forgot the people i've transact with andi need to scan my messeges in the inbox to remember. it might be good to have notes
I didn't find any good plugins for that, but you can to some extent probably emulate this using messages. You can create a new folder and move messages to it. If you want to make your own note (as opposed to just saving important conversations) you could send yourself a message and then move that message to your folder. I tested it and it works.
Of course, you can always use external resources for note taking as well.