code: public String mailbox(ImapRequestLineReader request) throws ProtocolException {
          String mailbox = astring(request);
          if (mailbox.equalsIgnoreCase(ImapConstants.INBOX_NAME)) {
              return ImapConstants.INBOX_NAME;
          } else {
              return BASE64MailboxDecoder.decode(mailbox);
          }
      }
docs: Reads a "mailbox" argument from the request. Not implemented *exactly* as per spec,
  since a quoted or literal "inbox" still yeilds "INBOX"
  (ie still case-insensitive if quoted or literal). I think this makes sense.
  <p/>
  mailbox         ::= "INBOX" / astring
  ;; INBOX is case-insensitive.  All case variants of
  ;; INBOX (e.g. "iNbOx") MUST be interpreted as INBOX
  ;; not as an astring.