She later realizes that she'll probably send essentially the same email to other recipients later. She uses the template many times. We design tests. We can get those at any time, and it makes no sense to keep track of the two obvious tests from that requirement until it's time to add the 120 other tests we'll get in the specification phase. We add requirements.
Testers are users of the product.
Our requirements are intended to allow us to extract product information that can't be gotten through the normal interface, or to control the system in ways that the normal interface makes difficult. But we'll have a better idea of what we need after we see what the normal interface does. It makes more sense for us to add our requirements during the specification phase. It will do no harm, since internal design will not have progressed very far. We make estimates.