This is how I try to send, email with sendmail command.
With html file in body and attached zip file.
The mail received is corrupted (without body and with corrupted attachment) .
(
echo "From: xxxx";
echo "To: balbal@mail.com";
echo "Subject: subject";
#echo "Content-Type: text/html";
echo "Content-Type: multipart/mixed; boundary=MAIL_BOUNDARY"
echo "MIME-Version: 1.0";
echo "--MAIL_BOUNDARY"
echo $message
cat myHtml.html
echo "--MAIL_BOUNDARY"
echo "Content-Type: application/zip"
echo "Content-Transfer-Encoding: base64"
echo "Content-Disposition: attachment; filename=zipfile.zip"
base64 zipfile.zip
echo "--MAIL_BOUNDARY--"
)> email.body
cat email.body | sendmail -t
mutt
or something that understands MIME