but I suspect it's more likely to be related to your client not doing MIME properly, as evidenced by the empty content-type header etc.
Ten's mail client (KMail) is using quoted-printable for plain text emails, which seems broken. It should only be necessary if there's 8bit text and a known dud mailserver, or lines of more than 1000 characters. Otherwise please use Content-Transfer-Encoding: 8bit and everyone's happy, give or take a few spare headers.