Erreur d'encodage

Quel type de paramètres utiliser pour éviter qu'un destinataire reçoive ce
type de message :

"
....
Subject: test 1
Mime-Version: 1.0
Content-Type: multipart/mixed; boundary="=_A485B716.CAABC7B4"

This is a MIME message. If you are reading this text, you may want to
consider changing to a mail reader or gateway that understands how to
properly handle MIME multipart messages.

--=_A485B716.CAABC7B4
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: quoted-printable
Content-Disposition: inline

test 1=20
sans pi=E8ce jointe
....
"

Cordialement