I dont know if Id even use that feature (I like my emails separated) but PLEASE get rid of that useless mailboxes list within each account! (The one with Trash, Sent, etc.)
I tap my mail account, then I have to tap Inbox on that useless middle screen. Then I have to go Back twice to get past that screen and back to my accounts list.
How often do I really want to get at my Trash or Drafts? Rarely. So dont offer them constantlyput them in a button, but get rid of the need to skip through that mailboxes list! So I can get to my Inbox (and back again) with one tap instead of two. I will be a happy man.