UnsubscribeBackgroundService (#7119)

Co-authored-by: Laila Bougria <[email protected]>
Co-authored-by: Adam Furmanek <[email protected]>

Author: 3 people

nservicebus/messaging/publish-subscribe/controlling-what-is-subscribed.md

@@ -56,3 +56,19 @@ Events can manually be subscribed and unsubscribed to:
 snippet: ExplicitSubscribe
 
 In NServiceBus version 6 and above, `Subscribe` and `Unsubscribe` are accessible via the `IMessageSession` available on the `IEndpointInstance` or within a [feature startup task](/nservicebus/pipeline/features.md#feature-startup-tasks).
+
+## Decomissioning event handlers
+
+An event is not automatically unsubscribed when a message handler is removed. The subscription remains active until it is unsubscribed.
+
+Unsubscribing can be done at startup via `IMessageSession.Unsubscribe`. For example, via a background service:
+
+```c#
+public sealed class UnsubscribeService(IMessageSession messageSession) : BackgroundService
+{
+	protected override async Task ExecuteAsync(CancellationToken stoppingToken)
+    {
+        await messageSession.Unsubscribe<MyEvent>();
+    }
+}
+```