There is no quicker way to put me off of your product than to start sending me emails as soon as I sign up to try it.
I understand the desire to create awareness and try to build habit. I used to think there was even some rationality in this. I now think it's all BS. A product shouldn't have to find artificial ways to remind you of its value.
I think 100% of this kind of energy is much better spent making the product so good that its impossible to forget about.