Livre-se do espaço após a vírgula:
SENDTO="[email protected],[email protected]"
Se isso não funcionar, tente usar o sendmail. Algo parecido com isto:
TMPFILE="/var/tmp/email_test"
EMAIL_SUB = "Subject: Your subject";
EMAIL_TO = "To: [email protected], [email protected]";
EMAIL_BCC = "Bcc: [email protected]";
echo "$EMAIL_TO" >> ${TMPFILE}
echo "$EMAIL_SUB" >> ${TMPFILE}
echo "$EMAIL_BCC" >> ${TMPFILE}
/usr/lib/sendmail -t < ${TMPFILE}