mda|learn|watch: support dropUniqueUnsubscribe config

List-Unsubscribe headers with unique identifiers (such as those
generated by our examples/unsubscribe.milter) should not
end up in public archives.  Add a new config knob to strip
List-Unsubscribe headers if they have the
`List-Unsubscribe-Post: List-Unsubscribe=One-Click'
header.

Unfortunately, this breaks DKIM signatures if the signature
covers either of these List-Unsubscribe* headers.  However,
breaking DKIM is the lesser evil compared to any archive reader
being able to stop archival by an independent archivist.

As much as I would like this to be the default, it probably
affects few users at the moment since very few mailing lists
use unique identifiers in List-Unsubscribe (but that number
has grown, recently).

1 files changed, 19 insertions, 0 deletions

diff --git a/Documentation/public-inbox-learn.pod b/Documentation/public-inbox-learn.pod
index f776df6b..b08e4bc8 100644
--- a/Documentation/public-inbox-learn.pod
+++ b/Documentation/public-inbox-learn.pod
@@ -73,6 +73,25 @@ Default: ~/.public-inbox/config
 
 =back
 
+=head1 CONFIGURATION
+
+These configuration knobs should be used in the
+L<public-inbox-config(5)> file.
+
+=over 8
+
+=item publicinboxImport.dropUniqueUnsubscribe
+
+=item publicinbox.<name>.address
+
+=item publicinbox.<name>.listid
+
+=item publicinboxmda.spamcheck
+
+See L<public-inbox-config(5)> for descriptions of these options
+
+=back
+
 =head1 CONTACT
 
 Feedback welcome via plain-text mail to L<mailto:meta@public-inbox.org>