etc: Add a skeleton configuration structure

This patch adds an "etc" directory, with a basic configuration structure
that can be used for an initial installation.

etc/chasquid/hooks/post-data

@@ -0,0 +1,55 @@
+#!/bin/bash
+#
+# This file is an example post-data hook that will run standard filtering
+# utilities if they are available.
+#
+#  - greylist (from greylistd) to do greylisting.
+#  - spamc (from Spamassassin) to filter spam.
+#  - clamdscan (from ClamAV) to filter virus.
+#
+# If it exits with code 20, it will be considered a permanent error.
+# Otherwise, temporary.
+
+set -e
+
+
+# Note greylistd needs you to add the user to the "greylist" group:
+#   usermod -a -G greylist mail
+if [ "$AUTH_AS" == "" ] && [ "$SPF_PASS" == "0" ] && \
+	command -v greylist >/dev/null && \
+	groups | grep -q greylist;
+then
+	REMOTE_IP=$(echo "$REMOTE_ADDR" | rev | cut -d : -f 2- | rev)
+	if ! greylist update "$REMOTE_IP" "$MAIL_FROM" 1>&2; then
+		echo "greylisted, please try again"
+		exit 75  # temporary error
+	fi
+	echo "X-Greylist: pass"
+fi
+
+
+TF="$(mktemp --tmpdir post-data-XXXXXXXXXX)"
+trap 'rm "$TF"' EXIT
+
+# Save the message to the temporary file, so we can pass it on to the various
+# filters.
+cat > "$TF"
+
+
+if command -v spamc >/dev/null; then
+        if ! SL=$(spamc -c - < "$TF") ; then
+                echo "spam detected"
+                exit 20  # permanent
+        fi
+        echo "X-Spam-Score: $SL"
+fi
+
+
+if command -v clamdscan >/dev/null; then
+        if ! clamdscan --no-summary --infected - < "$TF" 1>&2 ; then
+                echo "virus detected"
+                exit 20  # permanent
+        fi
+        echo "X-Virus-Scanned: pass"
+fi
+