>>> from email.header import Header, decode_header, make_header
>>> subject = '[ 201105161048 ] GewSt:=?UTF-8?B?IFdlZ2ZhbGwgZGVyIFZvcmzDpHVmaWdrZWl0?='
>>> h = make_header(decode_header(subject))
>>> str(h)
'[ 201105161048 ] GewSt: Wegfall der Vorläufigkeit'