Importing your data
Assuming that the subscribers have already consented to receiving email (via double-opt-in or some other mechanism provided by your previous subscriber), no! GDPR-wise, their existing consent carries over to Buttondown.
If you import a large number of subscribers, I'll temporarily disable your account so Buttondown can review the imported emails and make sure they're all up to code. The process shouldn't take more than a few hours!
Navigate to your settings page and click Import subscribers! You'll be prompted to upload a CSV:
Once you do so, you can map each column in your CSV, allowing you to bring in subscribers while keeping their existing tags, join dates, and metadata.
Adding a listserv?
Be sure that folks on the listserv are expecting the subscription: if one of them clicks to unsubscribe from the newsletter, it will affect the entire listserv (since from Buttondown's perspective, the listserv is a single subscriber.)