how to protect email from @domain.com to @domain.com from internet

[stiawan]

What you're seeing is known as backscatter or NDR spam, search the forums for the word 'backscatter' for some advice on reducing it.

Thank you for your information.
I have seach information about backscatter and found many URL.
And one important think is : Postfix-backscatter
so I know what is backscatter.

I have implement SPF on zimbra :
- /opt/zimbra/postfix/conf/master.cf.in
smtp inet n - n - - smtpd
#172.16.241.25:smtp inet n - n - - smtpd
-o content_filter=smtp-amavis:[127.0.0.1]:10024

- /opt/zimbra/conf/spamassassin/local.cf
score SPF_FAIL 10.000
score SPF_HELO_FAIL 10.000

And the result, every email scan with spf.
If someone send email using our domain spf will reject that email.

Aug 10 21:59:59 mailserver amavis[11205]: (11205-09) SPAM-TAG, <sam@36xxxx.com> -> <seger@my-domain.com>, No, score=-0.357 tagged_above=-10 required=6.6 tests=[BAYES_00=-2.599, DATE_IN_PAST_03_06=0.044, HTML_MESSAGE=0.001, MIME_HTML_ONLY=1.457, MIME_HTML_ONLY_MULTI=0.001, MONEY_BACK=0.001, MPART_ALT_DIFF=0.739, SPF_PASS=-0.001]