How do you mean "3 mailboxes"?
Three mailboxes on one address (the Inbox and two other folders)? Migration should have moved all mailboxes.
Three separate accounts (each with its own Inbox), perhaps as part of a MobileMe Family account? Each would have to be migrated separately.
Three incoming addresses (a main address with two mail aliases)? The aliases should have been migrated with the main address, but there are reports of some being left behind.
Unfortunately, you did need to migrate each portion of a family pack separately.
You should still be able to migrate the other two. Visit me.com/move and see if it offers you the chance to move an account to iCloud. I don't have any remaining family accounts to test it, but the residual MobileMe help system says migration should still work for a while.
Nope it's closed, my bad. If I upgrade to Lion will it offer to open a new mail account and I will just use the same settings? I read in one of the post that with the icloud native lion you can open a new account right from mail. True? I need to do something as my female partner is not very happy with me.
If you upgrade to Lion and create a new user account for your female partner, she should be able to use that to create a new iCloud account for herself. She might even be able to move the old MobileMe account if you move quickly enough.
Note that when you get to me.com/move there will a sentence below the "closed" sign indicating what you are still permitted to do. In some instances, that includes "move your account to iCloud" in addition to downloading files and photos. I see that phrase when I access it from my Lion system, even though I have moved all my MobileMe accounts to iCloud.