I get a lot of different emails every day, maybe because I have the habit of leaving my email on any website I consider somewhat interesting. And since I joined the maker community, the number of websites I consider interesting has rapidly increased, leaving me with an inbox that looks like this:
With an inbox of this magnitude, I get multiple emails along the lines of this every week:
Don't get me wrong, I love to get updates on what others are working on. My problem here is that I have no way of differentiating your product from the other fifty I signed up for, and there's no easy way to get more information either. Just because you've had your product on your head since you started working on it doesn't mean your users even remember what it is about.
If there's one thing I've learned from getting loads of these emails is that, unless your users login into your product every single day (i.e. Slack or GitHub), you have to remind your users what your product is when you email them.
Just add a subtle reminder when you first mention the name of the product (extra points if you link to the product), and you'll save your users some detective time.