Email Module date header needs time zone support

Ideas
1

When parsing timestamps in an email message, the parser should understand the timezone offset.
Since the standard class mapping ignores timezone, I built my own subclass. I suggest that the default header registry should map to a class like this which supports timezone data.

class DateClass(UnstructuredHeader):

    max_count = None
    value_parser = staticmethod(headparser.get_unstructured)

    @classmethod
    def parse(cls, hdrtext, kw):
        kw['parse_tree'] = cls.value_parser(hdrtext)
        kw['decoded'] = str(kw['parse_tree'])

    def init(self,*args,**kw):
        super().init(*args, **kw)
        timetext = str(self)
        try:
            timetuple = parsedate_tz(timetext)
            epochstart = datetime.fromisoformat('1970-01-01T00:00:00Z')
            newtime = mktime_tz(timetuple)
            self.timestamp = epochstart + timedelta(seconds=newtime)
        except:
            self.timestamp = None

# ========== End class definition ========================