We who email naturally worry about unsubscribers. We limit how much email we send for fear of wearing out patience and in the confident expectation of diminishing returns. That’s probably a good thing.
But there is evidence to suggest that, at least for certain brands, there is a better approach to optimizing email success. It comes down to sending as much as possible, while testing for diminishing returns. The Obama email team did this and found that, for them, there was no limit.