I have no e-mail lists, but some info: Make sure all you old and new subscribers have used double opt-in to subscribe. If not, send them a new invitation. You may lose some, but those are mostly not interested anyway. Delete the ones which do not reply.
If you are living in Germany, make sure you have a “Auftragsdatenverarbeitungs”-Agreement with your newsletter provider (Mailchimp offers those, for example).