gnus-treat-unfold-headers

gnus-treat-unfold-headers is a variable defined in `gnus-art.el'.
Its value is

head

Documentation:
Unfold folded header lines.
Valid values are nil, t, `head', `first', `last', an integer or a
predicate. See Info node `(gnus)Customizing Articles'.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 22.1 of Emacs.