I've installed a Zimbra 8.0.7, recently the server have become to deliver emails from accounts that belong to my domain ("example.com") but this mails come from external smtps, for example: 1. the emails accounts (only accounts from "example.com" server) receives emails from "admin@example .com" and this emails are not sent by our server, this emails came from external servers that "says" that are sending emails as our server, and our postfix are trying this emails as real emails and deliver this emails in inbox folder.
I'm wondering if there is any configuration on postfix to it performs same "DNS check" that realizes with external incoming emails but in the emails that receives from "example.com" sent by other ips?