Began work on unread msgs, harder than expected

Main issue is that I'm not 100% sure how I should arrange the schema,
choosing an array to begin with. Then, I'm trying to push an object into
the user's document that includes 'from, unread count and msg ids'. At
the moment the insertion is working ok, but not in the correct format -
I'm inserting a single 'from' value that is being overwritten, rather
than inserting an object with the 3 desired properties. I'm close, I can
feel it, I'm just missing a crucial part of the Mongodb syntax...

TBC...