This might seem a bit of a work-around, but can't you send it through a pipe on the localhost? The local mta interface ofcourse won't have any problems with converting this (seems qmail, so the fake sendmail binary or qmail-inject).

Something like (uh... I leave the conversion to perl as exercise ;) ):

#!/bin/sh

(       echo    "From: you@example.com"
        echo    "To: smb@example.net"
        echo -e "Subject: info\n"
        cat <<__EOF__

hmmz

__EOF__
) | /usr/sbin/sendmail smb@example.net
[download]

Good luck,

   wouter