Spam from same zimbra server

[mvalenzuela.cl]

zimbra mail categorized as spam sent from the same server to same domain. The public IP of my mail server is not blacklisted

[vavai]

Could you please to paste the header of message source of email which has identified as spam.

If you open it with Zimbra web mail, right click and then show original.

[abhiz]

it seems your network is hitted with backscatter.

[uxbod]

How can it be backscatter when it is from a local domain within the local server. Without seeing the headers from a email it is almost impossible to say; though I reckon the headers will show DNS_FROM_OPENWHOIS and FH_DATE_PAST_20XX are hitting. Therefore the OP should read the following threads :

[SOLVED] FH_DATE_PAST_20XX - Spamassassin bug - incorrect tagging from Jan 1, 2010 on
[SOLVED] spamassassin: false positives from openwhois