I have successfully imported and sent my subscribers the first newsletter, but if I want to import more subscribers, (these subscribers are from another plugin I have used before my website went live – From a Coming Soon Plugin) and avoid sending that first newsletter to those who have already received it, how can I be sure that I will only send the newsletter to just the fresh subscribers that I have imported for the second time? I don’t want to send the same newsletter twice.
You can use the preferences in the subscription form configuration panel. Create a preference and then import the new one assigning that preference. Then send a newsletter only to users with that preference active.