> Just to verify: do email headers *properly* define that this part of email is > "text/html" MIME type, and that it uses quoted-printable encoding?
Yes: ----_NmP-f79e46939889b5eb-Part_1 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: quoted-printable (I attached the gzipped spam in the previous mail)
