I attached file with Thai language filename. When I open mail it display attached file incorrectly. This is example of header:

------=_Part_4_816382.1138298620912
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: base64

4LiX4LiU4Liq4Lit4Lia4Liq4LmI4LiH4Lig4Liy4Lip4Liy4L mE4LiX4LiiICgwOjU5KQ==
------=_Part_4_816382.1138298620912
Content-Type: text/plain
Content-Transfer-Encoding: base64
Content-Disposition: attachment; filename="ıııııı.txt"