+ # examples/unsubscribe.milter and PublicInbox::Unsubscribe
+ 2369 => 'URLs as Meta-Syntax for Core Mail List Commands',
+ 8058 => 'Signaling One-Click Functionality for List Email Headers',
+
+ 1081 => 'Post Office Protocol – Version 3',
+ 1939 => 'Post Office Protocol – Version 3 (STD 53)',
+ 2449 => 'POP3 extension mechanism',
+ 2595 => 'STARTTLS for IMAP and POP3',
+ 2384 => 'POP URL Scheme',