Blueyonder email

My Daughter got an iPod Touch for Christmas and she can't put it down. I've set up her email but it won't work as it should. I have a UK Blueyonder (Virgin) account which has five mail boxes, named (for example's sake) 'mailbox', 'mailbox_2', 'mailbox_3', 'mailbox_4' and 'mailbox_5'

She has been allocated number 4 but when I put the name of that mailbox in the settings, it returns an 'email cannot be received' error. I can put in the straight 'mailbox' name, but that will then receive emails from ALL the 5 mailboxes at once - I only want her having access to her designated mailbox.

What am I doing wrong?