Content-Type: multipart/mixed; boundary="iamaboundary"

This is a text message in MIME format.
This part shouldn't appear in the output.

--iamaboundary
Content-Type: message/rfc822

Subject: I am a subject

This is a plain-text message.
--iamaboundary
Content-Type: message/global
Content-Transfer-Encoding: base64

U3ViamVjdDog56eB44Gv44CB5Lu25ZCN5Y2I5YmNDQoNCkkgYW0gYSBwbGFpbi10ZXh0IG1lc3NhZ2Uu
--iamaboundary
Content-Type: message/news
Content-Transfer-Encoding: quoted-printable

Subject: =e7=a7=81=e3=81=af=e3=80=81=e4=bb=b6=e5=90=8d=e5=8d=88=e5=89=8d

I am an encoded plain-text message.
--iamaboundary--