Content-Type: multipart/mixed; boundary=foo

--foo
Content-Transfer-Encoding: quoted-printable
Content-Type: text/plain; charset=utf-8

p=C3=A4iv=C3=A4=C3=A4

--foo
Content-Transfer-Encoding: base64
Content-Type: text/plain; charset=utf-8

ecO2dMOkIHZhYW4uCg== ignored
--foo
Content-Transfer-Encoding: base64
Content-Type: text/plain; charset=utf-8

?garbage
--foo--

