There was a time in the early days of the internet when spam, phishing, CEO impersonation, email trojans, and other forms of email abuse were not a thing. Mail servers would happily accept mail from any domain and forward it along to any other domain with no worry of being an unwitting accomplice in evildoing. Alas, those blissful days are long gone and, today, a mail server’s incoming mail policy is a critical early line of defense against these threats.
In this article, you will learn how to configure Postfix to enforce a simple mail acceptance policy for your domain(s). Your policy is determined by the role(s) your server will play (relay, destination, send-only, etc.), where your users typically connect from, and your tolerance for spam and misbehaving mail clients, among other considerations.
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The stairway begins to dissolve before your eyes, leaving a circular area with exits east and west, but remarkable mainly for its absence of a floor. Indeed, you find yourself standing in midair above a deep pit with the sort of comical look which is found mainly among duped cartoon characters.