Acquire contacts for your Newsletters from experts that are no longer active

Reach out to those people and authors who had relevant blogs on your field but that is no longer doing that. You can purchase their mailing lists for very cheap (since they probably don’t use it anymore) Approach people that you know have a list of relevant people that will actually be interested in your product/service and if possible also ask the author to send an initial introduction email to build credibility and increase the value of what you’ll send after.