gnus-save-all-headers

gnus-save-all-headers is a variable defined in `gnus-art.el'.
Its value is

t

Documentation:
*If non-nil, don't remove any headers before saving.
This will be overridden by the `:headers' property that the symbol of
the saver function, which is specified by `gnus-default-article-saver',
might have.

You can customize this variable.