You can see the list of all known push services in the whitelist file.
The hosts in the list are used by web browsers for implementing the Push API and Web Push.
The list of push service hosts is complete and covers all major browsers (Chrome, Firefox, Opera, Edge, Safari, etc.).
You can use this list for limiting outgoing connections to trusted hosts.
If you see a browser push service that is not in the list, feel free to open an issue or a pull request.