Adding upstream version 3.4.23.upstream/3.4.23upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/README_FILES/CONTENT_INSPECTION_README b/README_FILES/CONTENT_INSPECTION_README
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+PPoossttffiixx CCoonntteenntt IInnssppeeccttiioonn
+
+-------------------------------------------------------------------------------
+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.
+
+bbeeffoorree qquueeuuee,, bbuuiilltt--iinn,, lliigghhtt--wweeiigghhtt
+    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 BUILTIN_FILTER_README and
+    BACKSCATTER_README documents.
+
+aafftteerr qquueeuuee,, eexxtteerrnnaall,, hheeaavvyy--wweeiigghhtt
+    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 FILTER_README document.
+
+bbeeffoorree qquueeuuee,, eexxtteerrnnaall,, mmeeddiiuumm--wweeiigghhtt
+    The following two methods inspect mail BEFORE it is stored in the queue.
+
+      * The first method uses the SMTP protocol, and is described in the
+        SMTPD_PROXY_README document. This approach is available with Postfix
+        version 2.1 and later.
+
+      * The second method uses the Sendmail 8 Milter protocol, and is described
+        in the MILTER_README document. This approach is available with Postfix
+        version 2.3 and later.
+
+    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.
+
+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 http://
+www.postfix.org/, and on the postfix-users@postfix.org mailing list.
+