imap-use-utf7

imap-use-utf7 is a variable defined in `imap.el'.
Its value is

t

Documentation:
If non-nil, do utf7 encoding/decoding of mailbox names.
Since the UTF7 decoding currently only decodes into ISO-8859-1
characters, you may disable this decoding if you need to access UTF7
encoded mailboxes which doesn't translate into ISO-8859-1.

You can customize this variable.