/usr/lib/ruby/vendor_ruby/mime/types/message.obsolete is in ruby-mime-types 1.25-1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | !message/news :8bit 'IANA,RFC1036,[H.Spencer]
!message/vnd.si.simp 'IANA,[Parks Young=ParksYoung]
|