You should definitely not send 25 emails a week. I wouldn't advise that. Just so you understand where I am coming from: We have been sending 4 emails per year in the past. To improve the quality and quantity of emails we send I have done this research and shared this knowledge in the post.

When I signed up for loggly they sent me one email every day for a month. I could have unsubscribed but I didn't. Because the emails contained tutorials about the service and I wanted to know more about how their service worked. I can't say I read every email, but I have at least took a glance of the screenshots in the tutorials. So, sometimes if you like the product you want to receive emails. It is a good thing as long as it is extremely easy to unsubscribe.