When a notifier is registered, it can provide information about additional properties that must be filled in by the user. To obtain values of these properties, use the following code:
String value = user.getPropertyValue(new NotificatorPropertyKey(<notifier type>, <property name>));
Notifier can also provide custom UI for Notifier rules and My Settings&Tools pages. See PlaceId.NOTIFIER_SETTINGS_FRAGMENT and PlaceId.MY_SETTINGS_NOTIFIER_SECTION.
Use source code of the existing plugins as a reference: