looking for a way to let 2 people message each other in private blog

I am setting up a store to sell other sellers items. When someone buys an item I would like a private wordpress blog created (it does not need heavy security) In that blog the two people involved (buyer and seller) will both receive email notifications of posts and be able to post replies WITHOUT needing to login or set up an account. I also need the ability for attachment upload.

I am fairly new to WordPress, any advice on if this is possible and where to start?