In Kunversion, you can have newsletters sent out to all of your "Sphere" status Leads. 

Newsletters are compiled from your blog posts as well as some filler content generated by us. So, maintaining a blog means that you'll have fresh content for your entire sphere every month!

There are no restrictions apart from the fact that they only go out to your Sphere status Leads, and those Leads must be subscribed.
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If you do not maintain a new blog post at least once a month, your newsletter will not send.