WordPress can send pingbacks to sites you link to. While self-pings can help connect related articles on your own site, you may not want WordPress notifying external sites whenever you publish a link. Only Self Pings restricts outgoing pingbacks to your own site or to explicitly approved URLs.

With no saved settings, it allows your current public site URL and URLs beneath it. You can replace this list with the URLs you want to allow under Settings > Only Self Pings.

Small plugin with no external service, JavaScript, tracking or front-end assets.
Works with links processed by WordPress’s normal pingback system, independently of the editor used to write a post.
Retains settings from version 1.0.
Supports per-site settings when network activated on Multisite.

The plugin does not enable pingbacks. Outgoing notifications must be enabled in WordPress, and the receiving article must accept pingbacks.