The user can send a ReceiveMessage request to example_queue, the IAM policy allows this action

If you add a policy that denies the user access to all actions for the queue, the policy will override the other two policies and the user will not have access to example_queue

If the user sends a SendMessage request to example_queue, the IAM policy will deny this action

Either of IAM policies or Amazon SQS policies should be used to grant permissions. Both cannot be used together

Adding only an IAM policy to deny the user of all actions on the queue is not enough. The SQS policy should also explicitly deny all action