'Retrieve a date field from a header as a 10-tuple.
The first 9 elements make up a tuple compatible with time.mktime(),
and the 10th is the offset of the poster\'s time zone from GMT/UTC.'

def getdate_tz(self, name):

    try:
        data = self[name]
    except KeyError:
        return None
    return parsedate_tz(data)
