gnus-treat-fill-long-lines

gnus-treat-fill-long-lines is a variable defined in `gnus-art.el'.
Its value is

(typep "text/plain")

Documentation:
Fill long 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 24.1 of Emacs.