'Retrieve the internal date associated with one or more messages
This command is allowed in the Selected state.
@type messages: C{MessageSet} or L{str}
@param messages: The messages for which to retrieve the internal date.
@type uid: C{bool}
@param uid: Indicates whether the message sequence set is of message
numbers or of unique message IDs.
@rtype: C{Deferred}
@return: A deferred whose callback is invoked with a dict mapping
message numbers to date strings, or whose errback is invoked
if there is an error.  Date strings take the format of
"day-month-year time timezone".'

def fetchInternalDate(self, messages, uid=0):

    return self._fetch(str(messages), useUID=uid, internaldate=1)
