How long the telemetry of a single message will be retained on Azure Notification Hub? Should we get the telemetry and store offline if we want to trace a message 7 days later?
Telemetry is retained by the system for 30 days. Also worth noting that notification telemetry is only available when on the Standard SKU.
I see now that this value doesn't appear to be documented. I'll see if I can get the Notification Hubs documents updated to properly reflect this. Thank you for raising the question.