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| author | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-06 01:46:30 +0000 |
|---|---|---|
| committer | Daniel Baumann <daniel.baumann@progress-linux.org> | 2024-05-06 01:46:30 +0000 |
| commit | b5896ba9f6047e7031e2bdee0622d543e11a6734 (patch) | |
| tree | fd7b460593a2fee1be579bec5697e6d887ea3421 /html/CONTENT_INSPECTION_README.html | |
| parent | Initial commit. (diff) | |
| download | postfix-upstream/3.4.23.tar.xz postfix-upstream/3.4.23.zip | |
Adding upstream version 3.4.23.upstream/3.4.23upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'html/CONTENT_INSPECTION_README.html')
| -rw-r--r-- | html/CONTENT_INSPECTION_README.html | 92 |
1 files changed, 92 insertions, 0 deletions
diff --git a/html/CONTENT_INSPECTION_README.html b/html/CONTENT_INSPECTION_README.html new file mode 100644 index 0000000..d44c54b --- /dev/null +++ b/html/CONTENT_INSPECTION_README.html @@ -0,0 +1,92 @@ +<!doctype html public "-//W3C//DTD HTML 4.01 Transitional//EN" + "http://www.w3.org/TR/html4/loose.dtd"> + +<html> + +<head> + +<title>Postfix Content Inspection </title> + +<meta http-equiv="Content-Type" content="text/html; charset=us-ascii"> + +</head> + +<body> + +<h1><img src="postfix-logo.jpg" width="203" height="98" ALT="">Postfix +Content Inspection </h1> + +<hr> + +<p> Postfix supports three content inspection methods, ranging from +light-weight one-line-at-a-time scanning before mail is queued, to +heavy duty machinery that does sophisticated content analysis after +mail is queued. Each approach serves a different purpose. </p> + +<dl> + +<dt> <b> before queue, built-in, light-weight</b> </dt> + +<dd> <p> This method inspects mail BEFORE it is stored in the queue, +and uses Postfix's built-in message header and message body +inspection. Although the main purpose is to stop a specific flood +of mail from worms or viruses, it is also useful to block a flood +of bounced junk email and email notifications from virus detection +systems. The built-in regular expressions are not meant to implement +general SPAM and virus detection. For that, you should use one of +the content inspection methods described below. Details are described +in the <a href="BUILTIN_FILTER_README.html">BUILTIN_FILTER_README</a> and <a href="BACKSCATTER_README.html">BACKSCATTER_README</a> documents. +</p> + +<dt> <b> after queue, external, heavy-weight</b> </dt> + +<dd> <p> This method inspects mail AFTER it is stored in the queue, +and uses standard protocols such as SMTP or "pipe to command and +wait for exit status". After-queue inspection allows you to use +content filters of arbitrary complexity without causing timeouts +while receiving mail, and without running out of memory resources +under a peak load. Details of this approach are in the <a href="FILTER_README.html">FILTER_README</a> +document. </p> + +<dt> <b> before queue, external, medium-weight</b> </dt> + +<dd> <p> The following two methods inspect mail BEFORE it is stored in the +queue. </p> + +<ul> + +<li> <p> The first method uses the SMTP protocol, and is described +in the <a href="SMTPD_PROXY_README.html">SMTPD_PROXY_README</a> document. This approach is available +with Postfix version 2.1 and later. </p> + +<li> <p> The second method uses the Sendmail 8 Milter protocol, and +is described in the <a href="MILTER_README.html">MILTER_README</a> document. This approach is +available with Postfix version 2.3 and later. </p> + +</ul> + +<p> Although these approaches appear to be attractive, they have +some serious limitations that you need to be aware of. First, +content inspection software must finish in a limited amount of time; +if content inspection needs too much time then incoming mail +deliveries will time out. Second, content inspection software must +run in a limited amount of memory; if content inspection needs too +much memory then software will crash under a peak load. Before-queue +inspection limits the peak load that your system can handle, and +limits the sophistication of the content filter that you can use. +</p> + +</dl> + +<p> The more sophisticated content filtering software is not built +into Postfix for good reasons: writing an MTA requires different +skills than writing a SPAM or virus killer. Postfix encourages the +use of external filters and standard protocols because this allows +you to choose the best MTA and the best content inspection software +for your purpose. Information about external content inspection +software can be found on the Postfix website at <a href="http://www.postfix.org/">http://www.postfix.org/</a>, +and on the postfix-users@postfix.org mailing list. </p> + +</body> + +</html> |