I've been looking for one but can't find anything.
I'm a previous blackberry user who has 8+ email accounts.
My blackberry had an inbox at which ALL of the emails appeared from all email accounts.
Didn't matter which account it was received on, they would end up in this large basket of emails. (In addition to individual baskets)
currently I have to switch accounts to see emails from respective accounts which is a pain in the butt when you have so many.