The operative word here is “done”. First, you are never done testing because the winner is the new control and you will always need to be thinking of ways to beat the control. Second, your email program is in a constant state of change and you need to be rolling with that change.
Having a “we are done” mentality leads to complacency and while you might think you are done, I can guarantee that other email marketers are never done. Remember…you can never forget about what your competitors are doing, but the focus should be on what you’re doing, since you are always competing for subscribers time in the inbox.
Don’t be done. Be unfinished.