dkim_responder(1) on Linux
The text 3c7e96d4d1d0, as Debian 10 (Buster), Debian 9 (Stretch), Debian 8 (Jessie), Debian 7 (Wheezy), Debian 6.0 (Squeeze) shipped it. The page shows this text now.
filters incoming email traffic according to the domain keys specifications