21- clean all FIXME
79- support other mailbox format like mh, maildir, Mail.app, etc.
82- introduce exceptions (and handlers) in most classes
85- allow subfolder support in LocalStore/LocalFolder
87- Add Mail-Followup-To support (see IETF draft)
88- maybe use iconv on both GNUstep and Cocoa to convert unsupported
    encodings by NSString to UTF-8.
89- Add [Part -initWithData: charset:] so that people can chose
    which charset to fallback to when none has been specified for 8-bit
    message.
