'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 ValueError or IndexError: When the index does not correspond to
a message in the mailbox.  The use of ValueError is preferred.'

def getUidl(self, i):

    raise ValueError
