From phpBB Development Wiki
This might need to be split into multiple components
Generic Messaging Service
Allows sending messages / notifications via any of the available protocols. Should also allow sending with multiple protocols. This should be used whenever a user is informed about any process within phpBB. Based on the user's settings or selections the notification will be send with the prefered protocol.
Concrete Protocol Services
One could add a service that creates posts in a forum on the board. This might make sense for notifications about moderation activities.