One recommended way to help secure your Postfix mail server is enabling TLS (Transport Layer Security) for connections to and from Postfix. You can search for more detailed descriptions of exactly how TLS works, but basically it
It relies on a key and a certificate to help accomplish its purposes, and this article will walk you through generating a key, getting your certificate, and installing everything on your Postfix system to enable TLS/SSL for SMTP connections.

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