Offline messaging between a repository storage operation cell and one or more mobile/remote storage operation cells is disclosed. The repository cell is managed by a repository storage manager that communicates to and from the remote cell via a specially-configured media agent. The illustrative intermediary media agent is configured to: queue messages directed to the remote cell, process them according to applicable parameters (e.g., time-to-live constraints, updates, cancellations, etc.), and transmit the processed messages to the remote cell when connectivity is available. The intermediary media agent also relays messages from the remote cell to the repository, including responses by the remote to the processed messages received from the repository via the intermediary media agent.