We are a private detective agency and one of the services that we offer is mobile fingerprinting. Our technicians go to the businesses and fingerprint the employees. Most of our clients are insurance companies, financial services, non-profit organizations and governmental agencies, to name a few.
First of all, I would think about what your email marketing goals are. Are you trying to generate sales, connect with your audience, get feedback, or all of the above?
One of the best practices I swear by is keeping in regular contact with your subscribers by emailing them useful content once every week/fortnight. So in your case, could you talk about security concerns related to the finance or insurance industry? The Apple vs. FBI debate is an interesting and current discussion you could weigh in on.
As you deliver your content, you could then plug your fingerprinting service and talk about the benefits of this for your clients.
Hope this helps!