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When you clone a message it becomes a new message, that means system properties are not cloned which gives the cloned message a fresh delivery count starting at 1 again. See also https://docs.azure.cn/zh-cn/dotnet/api/microsoft.azure.servicebus.message.clone?view=azure-dotnet

You can look into the Peek Lock Feature of Azure Service Bus. When using PeekLock the message gets invisible on the queue until you explicitly abandon it (put it back to the queue with delivery count increased) or complete if everything works out as expected when processing the message. Another option is to explicitly dead letter this message.

The feature is documented here: https://docs.microsoft.com/en-us/azure/service-bus-messaging/message-transfers-locks-settlement#peeklock

But the important thing about this is that if you do not perform any of the above mentioned actions such as cloning Azure Service Bus will automatically make the message visible again after a defined interval (the LockDuration property) or when you abandon it.

So to get a delayed retry and dead letter behaviour (when maximum delivery count has been reached) you can use the following options:

Option 1. Retry via Azure service bus auto-unlock

When processing of the message cannot be performed at the moment for some reason catch the exception and make sure none of the mentioned actions (abandon, complete or deadletter) are performed. This will keep the message invisible for the remaining time and will make it again visible after the configured lock duration has been reached. And the delivery count will also be increased by Azure Service Bus as expected.

Option 2. Implement your own retry policy

Perform your own retry policy in your code and retry processing of the message. If your maximum retries have been reached abandon the message which will make it visible again for the next queue reading step after the retry time has been reached. In this case the delivery count is increased as well.

Note: If you choose option 2.) make sure your retry period will conform to the defined LockDuration so that your message will not be visible again on the queue if you are still processing it with retries. You could also renew the lock between retries by calling the RenewLock() method on the message between retries.

If you implement the retry policy in your code I recommend using into Polly .Net which already gives you great features such as Retry and Circuit Breaker policies. See https://github.com/App-vNext/Polly