Existing e-mail lists are a resource not be ignored when launching a business blog.
Brian Clark published a case study of an e-learning blog that converted the company’s existing contacts into thousands of subscribers – on the first day.
Another way they drove people to subscribe was to offer a white paper on a topic that has value to the target audience.
E-mail may be so 1990s, but that doesn’t mean it doesn’t still work as a way to reach a targeted group quickly. Clark also made sure the landing page included an option for people to subscribe to an e-mail alert of each blog post.
Remember, if you’re reaching people by e-mail, they may want to continue to be connected by e-mail. It’s a lesson that too many people forget. (I’m thinking of several websites that allow me to phone a customer service person, but won’t let me send an e-mail or fill in a "contact us" form.)
As for whether you can keep your subscribers, that requires ongoing effort to provide something of value.