'Get a unique identifier for a message.
@type i: L{int}
@param i: The 0-based index of a message.
@rtype: L{bytes}
@return: A string of printable characters uniquely identifying the
message for all time.
@raise IndexError: When the index does not correspond to a message in
the mailbox.'

def getUidl(self, i):

    base = os.path.basename(self.list[i])
    return md5(base).hexdigest()
