newsletter with export email to csv and import from csv features
Here's how to do that:


Install Views (you probably have this installed already).
Install Views data export module.
Create a new view that will show either "Simplenews subscriber" or "Simplenews subscription".
Add a new display of "Data export" type to that view. There you can choose the format (.csv, .doc, .txt, etc.) and configure other settings. Don't forget to set "Attach to" value to the page display you created in step #3.