'Add to the set flags for one or more messages.
This command is allowed in the Selected state.
@type messages: C{MessageSet} or L{str}
@param messages: A message sequence set
@type flags: Any iterable of L{str}
@param flags: The flags to set
@type silent: C{bool}
@param silent: If true, cause the server to suppress its verbose
response.
@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 list of the
server\'s responses (C{[]} if C{silent} is true) or whose
errback is invoked if there is an error.'

def addFlags(self, messages, flags, silent=1, uid=0):

    return self._store(messages, '+FLAGS', silent, flags, uid)
