We are trying to implement a notification module. It allows website internal users to send message to each other. A key feature is that it allows business users to send bulk messages to the users. We are talking about millions of users here.
Currently it is planned to be a publish/subscribe model. Once login, system shall retrieve the relevant messages for the user from a database table. The logic gets more and more complicated when each users are allow to delete and reply to the message he/she received.
Pubsubhub seems to be more server to server. XMPP seems to be too complicated for this scenario.
Anything I miss out? Can I make it simpler? Any existing library to build on? I'm open to any suggestions.