You have uninstalled an agent from the endpoint, but you are still receiving offline alerts from kaseya.
The important thing to note here is that the Kaseya server itself sends these messages based on the "last check-in time in the database for that agent. If the kaseya server sees that the time between the last check-in time and the current time has exceeded your threshold, then it will generate these emails.
There are a couple of approaches.
1. Go to the agent tab -> delete function. Select the agent, which will be showing offline, and delete it - making sure that you select the "delete now without uninstalling agent". This will remove the agent from the database and all the corresponding alerts configured for it.
This will remove all the data about this machine, so this should not be used if you wish to keep the information about the agent, such as audit or patch data.
2. Go to the Monitor tab -> alerts page. Select the agent in question and use the "Clear" button to remove the alert from the machine.
This will leave the agent behind with all the data still in the database, but the server will no longer generate alerts for this agent.
3. Go to the Monitor Tab -> Suspend Alarms. If the agent if offline for a known reason and you intend for it to be used again in future, you can simply suspend the alarms. This stops all alerts for this agent. This is typically used for scheduled outages, but will work for this situation also.