bad ciphers were allowed in smtp submssion

This disallows aNULL and other bad ciphers in the Postfix submission server.

I missed an option in 45e93f7d recommended by the blog post I was reading.

Fixes #389.

setup/mail-postfix.sh

@@ -75,7 +75,7 @@ tools/editconf.py /etc/postfix/master.cf -s -w \
 	"submission=inet n       -       -       -       -       smtpd
 	  -o syslog_name=postfix/submission
 	  -o smtpd_milters=inet:127.0.0.1:8891
-	  -o smtpd_tls_ciphers=high -o smtpd_tls_protocols=!SSLv2,!SSLv3
+	  -o smtpd_tls_ciphers=high -o smtpd_tls_exclude_ciphers=aNULL,DES,3DES,MD5,DES+MD5,RC4 -o smtpd_tls_protocols=!SSLv2,!SSLv3
 	  -o cleanup_service_name=authclean" \
 	"authclean=unix  n       -       -       -       0       cleanup
 	  -o header_checks=pcre:/etc/postfix/outgoing_mail_header_filters"