Shoutbox

All accounts are listed in registry under
HKEY_CURRENT_USER\Software\Microsoft\Internet Account Manager\Accounts\
HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\UnreadMail
HKEY_USERS\S-1-5-21-1409082233-152049171-1957994488-500\Software\Microsoft\Internet Account Manager\Accounts
HKEY_USERS\S-1-5-21-1409082233-152049171-1957994488-500\Software\Microsoft\Windows\CurrentVersion\UnreadMail

Try to remove those accounts there. Those S-1-5.... numbers can be different for you.
And when you remove accounts, all dbx files releated to those accounts should get deleted too.