How do I block unwanted messages from outside my host?

Exim uses Access Control Lists (ACLs) for controlling incoming mail from other hosts. A whole chapter in the reference manual is devoted to describing how they work. A wide variety of conditions can be imposed on incoming messages. The default Exim run time configuration contains an example of an ACL which blocks all relaying, and messages whose senders cannot be verified. This example is heavily commented and worth studying.

See also How do I stop Exim being an open relay?

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