Most of spam email sent from public IP who did not have PTR/Reverse DNS. What is PTR/Reverse DNS, you can find more information from Wikipedia 😀 : https://en.wikipedia.org/wiki/Reverse_DNS_lookup If you have Zimbra and want to enable PTR/Reverse DNS lookup for incoming, you can perform the following command su – zimbra zmprov mcf +zimbraMtaRestriction "reject_unknown_client_hostname" Please wait ..
From previous article, you can configure and validate DKIM records on Zimbra which is used to increase email reputation. The configuration will increase reputation for outgoing email. But, how to enable DKIM/DomainKeys checking for incoming connection? By enable DKIM/DomainKeys checking, you can reject every incoming email who did not have DKIM/DomainKeys. By default, Zimbra only configure OpenDKIM as ..