gnus: Fancy splitting to parent

 
 9.18.3 Fancy splitting to parent
 --------------------------------
 
 Simply put, this lets you put followup e-mail where it belongs.
 
    Every message has a Message-ID, which is unique, and the registry
 remembers it.  When the message is moved or copied, the registry will
 notice this and offer the new group as a choice to the splitting
 strategy.
 
    When a followup is made, usually it mentions the original message’s
 Message-ID in the headers.  The registry knows this and uses that
 mention to find the group where the original message lives.  You only
 have to put a rule like this:
 
      (setq nnimap-my-split-fancy '(|
 
            ;; split to parent: you need this
            (: gnus-registry-split-fancy-with-parent)
 
            ;; other rules, as an example
            (: spam-split)
            ;; default mailbox
            "mail")
 
    in your fancy split setup.  In addition, you may want to customize
 the following variables.
 
  -- Variable: gnus-registry-track-extra
      This is a list of symbols, so it’s best to change it from the
      Customize interface.  By default it’s ‘(subject sender recipient)’,
      which may work for you.  It can be annoying if your mail flow is
      large and people don’t stick to the same groups.
 
      When you decide to stop tracking any of those extra data, you can
      use the command ‘gnus-registry-remove-extra-data’ to purge it from
      the existing registry entries.
 
  -- Variable: gnus-registry-split-strategy
      This is a symbol, so it’s best to change it from the Customize
      interface.  By default it’s ‘nil’, but you may want to set it to
      ‘majority’ or ‘first’ to split by sender or subject based on the
      majority of matches or on the first found.  I find ‘majority’ works
      best.