![]() SMTP server process after logging its findings. Skip tests, postscreen(8) minimizes its impact on legitimate emailīy default, postscreen(8) hands off all connections to a Postfix postscreen(8) maintains a temporary allowlist forĬlients that pass its tests by allowing allowlisted clients to Some tests introduce a delay ofĪ few seconds. General operationįor each connection from an SMTP client, postscreen(8) performs Content is not a good indicatorįor making is-a-zombie decisions based on single measurements,Īnd that is the problem that postscreen(8) is focused on. Message contentĬan vary from one delivery to the next, especially with clients Postscreen(8) does not inspect message content. Indicators for making is-a-zombie decisions based on single Second, postscreen(8) looks for protocolĬompromises that are made to speed up delivery. First, postscreen(8) determines if the remote SMTP client Postscreen(8) uses a variety of measurements to recognize Mail even when the server tells them to go away. Or they ignore responses from SMTP servers and continue sending For example, they speak before their turn, To speed up spam deliveries, zombies make compromises in their SMTP Of time to deliver spam before their IP address becomes denylisted. Zombies have challenges too: they have only a limited amount ![]() Not-a-zombie, it allowlists the client temporarily to avoid further Once postscreen(8) decides that a client is Many zombies try to fly under the radar and avoid spamming the same The main challenge for postscreen(8) is to make an is-a-zombieĭecision based on a single measurement. Spending most of its resources not receiving email. Tool like postscreen(8) that keeps the zombies away, Postfix would be Problem will get worse before things improve, if ever. Most email is spam, and most spam is sent out by zombies (malware Historical notes and credits The basic idea behind postscreen(8). ![]()
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