It may be that now you’re thinking “Wow, I need to e-mail my users!” Yet, because of the way the Linux app community works, it’s extremely likely you only know a few actual users of your app. There may be thousands of users out there that have your app installed, maybe using it every day, but you don’t know who they are. But no lists means fewer calls for donations and less interaction with your users.
The answer to how you get an email list for a newsletter, etc. is to start a newsletter and add a signup form on your site. Promise to keep them updated on new plug-ins and releases. Yes it will take time.
Make sure your site is mentioned in your app so people can find you and start sending out content that is valuable. Reuse the content on your site to improve your search engine ranking while you’re at it.
Below is an example for the “Classics” iPhone app sign up form to be notified when it was released:
Obviously, their site and email are beautiful and that of course helps.