Customized and personal emails convert the best. Send out emails to your users yourself and ask them to contact you directly should they have any questions. This kind of relationship building goes a long way, and will help make them your dedicated users.
Also, send out "event" emails (emails that would require an action from the user) with your name (instead of your company's name). This would give you much higher click through rate because your users will feel like the mail came from you, and not from a server.
Another tip for event emails is to not use any tempate. Use the default white background email template and don't use "Dear XXX" to start out your email. Even "Hey!" is better. Again, users are now immune to emails with a beautiful template, so that keep it simple and human.
