By default, WordPress does not let you to automatically add nofollow to external links. You will have to manually add it or use a plugin to do this in an easier way.
Nofollow for external link
Use this plugin https://wordpress.org/plugins/nofollow-for-external-link/, and rel=nofollow and target=_blank will be automatically inserted, for all external links of the site posts or page.
You can also exclude domains by not to adding rel=nofollow for the selected external links.
- The plugin will not add rel=nofollow or target=_blank to any internal link on your website posts/pages.
- If you previously added manually, rel=dofollow or rel=nofollow to any post , the plugin will not add rel=nofollow for that post.
- If you previously added manually, target=_blank to any post, the plugin will not add target=_blank for that post.
– very easy to setup