A notification service may act as an intermediary between sources of text-based communications (e.g., message channels within a communication and collaboration platform) and the intended recipients of action items contained in messages posted to these sources. The notification service may store, for each action item, an instance of a universal actionable notification data structure specifying, among other things, response options for the action items, and may, for a specific user, aggregate action items intended for that user across multiple sources, aggregate and send notification messages generated from the respective instances of the universal actionable notification data structures to a central notification inbox accessible by the user, and upon receipt of a response from the user, generate and post a response message to the source from which the action item originated.