Asn Zimbra -

# Example: Block a spammy ASN range 192.0.2.0/24 REJECT Spam from ASN 12345 203.0.113.0/24 REJECT Spam from ASN 67890

You will see something like: origin: AS15169 (Google’s ASN). Zimbra does not have a GUI for ASN filtering, but you can configure Postfix directly. asn zimbra

Edit /opt/zimbra/common/conf/postfix_asn_blacklist Add the ASN netblocks (you must expand ASN to CIDR ranges manually or via script): # Example: Block a spammy ASN range 192