Mutt has the command ‘h’ to hide (weed) most of the headers in emails. After an upgrade to 1.12.0 I found this wasn’t working. I emailed Stuart Henderson, the maintainer of the Mutt package for OpenBSD. He thinks this is due to a change in the code of the new version of Mutt. He advised including these lines in .muttrc:
unignore From To CC Subject Date Reply-To Organization X-Mailer User-Agent Organisation Organization Priority Importance Mail-Followup-To
This makes ‘c’ work correctly. Thanks, Stuart.
Note added 31 May: Stuart has sent me a link which explains how the problem arose (https://gitlab.com/muttmua/mutt/issues/144). The change appeared in 1.12.0 but has now been reversed in 1.12.1 so the above lines are no longer needed.