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How do I block in-bound mail from masquerading as coming from an internal network?

April 26, 2017block coming in-bound Internal mail Masquerading Network

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How do I block in-bound mail from masquerading as coming from an internal network?

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The no_inbound_from domain directive will block e-mail that originates from an unprotected network network but uses the domain name in either the SMTP “MAIL From:” command or a “From:” header line. This allows the user to specify domains that should not appear in the MAIL FROM or From: addresses in an inbound mail originated from outside the protected network. A 550 response code is sent and connection terminated if violation is found.