Using Sendmail as my SMTP server I receive similar results to you if I do not include my ISPs smtp server name in my sendmail.mc
config file even though my server is naturally connected via their broadband line.... Give it a try
See below for the header info. in my sendmail.mc
dnl # This is the sendmail macro config file for m4. If you make changes to
dnl # /etc/mail/sendmail.mc, you will need to regenerate the
dnl # /etc/mail/sendmail.cf file by confirming that the sendmail-cf package is
dnl # installed and then performing a
dnl # /etc/mail/make
VERSIONID(`setup for linux')dnl
dnl # Do not advertize sendmail version.
dnl define(`confSMTP_LOGIN_MSG', `$j Sendmail; $b')dnl
dnl # default logging level is 9, you might want to set it higher to
dnl # debug the configuration
dnl define(`confLOG_LEVEL', `9')dnl
dnl # Uncomment and edit the following line if your outgoing mail needs to
dnl # be sent out through an external mail server:
dnl define(`SMART_HOST', `smtp.ispserver.com'
I ran the mail server test per your link - very intuitive - I achieved a result of 90% - Very Strong Security
with a percentile score of 94%
meaning that my sever is in the top 6% of all severs that they have ran the test against - Heck Yeah!!! The areas where I didn't receive a point or was deducted are fortunately not significant for me. Am I now tempting fate by publishing this result? - Oops, I hope not.....