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diff --git a/src/transport-filter.src b/src/transport-filter.src
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+#! PERL_COMMAND
+
+# This is a Perl script to demonstrate the possibilities of on-the-fly
+# delivery filtering in Exim. It is presented with a message on its standard
+# input, and must copy it to the standard output, transforming it as it
+# pleases, but of course it must keep to the syntax of RFC 822 for the headers.
+
+# The filter is run before any SMTP-specific processing, such as turning
+# \n into \r\n and escaping lines beginning with a dot.
+#
+# Philip Hazel, May 1997
+#############################################################################
+
+use warnings;
+BEGIN { pop @INC if $INC[-1] eq '.' };
+use File::Basename;
+
+if ($ARGV[0] eq '--version') {
+    print basename($0) . ": $0\n",
+        "build: EXIM_RELEASE_VERSIONEXIM_VARIANT_VERSION\n",
+        "perl(runtime): $]\n";
+        exit 0;
+}
+
+# If the filter is called with any arguments, insert them into the message
+# as X-Arg headers, just to verify what they are.
+
+for ($ac = 0; $ac < @ARGV; $ac++)
+  {
+  printf("X-Arg%d: %s\n", $ac, $ARGV[$ac]);
+  }
+
+# Now read the header portion of the message; this is easy to do in Perl
+
+$/ = "";                    # set paragraph mode
+chomp($headers = <STDIN>);  # read a paragraph, remove trailing newlines
+$/ = "\n";                  # unset paragraph mode
+
+# Splitting up a sequence of unique headers is easy to do in Perl, but a
+# message may contain duplicate headers of various kinds. It is better
+# to extract the headers one wants from the whole paragraph, do any appropriate
+# munging, and then put them back (unless removing them altogether). Messing
+# with "Received:" headers is not in any case to be encouraged.
+
+# As a demonstration, we extract the "From:" header, add a textual comment
+# to it, and put it back.
+
+($pre, $from, $post) =
+  $headers =~ /^(|(?:.|\n)+\n)   (?# Stuff preceding the From header,
+                                     which is either null, or any number
+                                     of characters, including \n, ending
+                                     with \n.)
+               From:[\s\t]*      (?# Header name, with optional space or tab.)
+               ((?:.|\n)*?)      (?# Header body, which contains any chars,
+                                     including \n, but we want to make it as
+                                     short as possible so as not to include
+                                     following headers by mistake.)
+               (|\n\S(?:.|\n)*)$ (?# Header terminates at end or at \n followed
+                                     by a non-whitespace character and
+                                     remaining headers.)
+              /ix;                #  case independent, regular expression,
+                                  #  use extended features (ignore whitespace)
+
+# Only do something if there was a From: header, of course. It has been
+# extracted without the final \n, which is on the front of the $post
+# variable.
+
+if ($pre)
+  {
+  $headers = $pre . "From: $from (this is an added comment)" . $post;
+  }
+
+# Add a new header to the end of the headers; remember that the final
+# \n isn't there.
+
+$headers .= "\nX-Comment: Message munged";
+
+# Write out the processed headers, plus a blank line to separate them from
+# the body.
+
+printf(STDOUT "%s\n\n", $headers);
+
+# As a demonstration of munging the body of a message, reverse all the
+# characters in each line.
+
+while (<STDIN>)
+  {
+  chomp;
+  $_ = reverse($_);
+  printf(STDOUT "%s\n", $_);
+  }
+
+# End