Wow, a base with 18 million crypto investors. If this were true, I'm not sure you need to look for clients for it. There are so many possibilities to monetise such a resource.
Have you thought about offering a free demo to get some feedback on the quality of your service? How do we know that these are real email addresses, and not fake or alternative ones that many people use to select spam
for your understanding: for mailing you need to buy a server, a domain, set them up. write adaptive HTML. this costs money and it takes time. it can't be free. for a test we have sending 100k emails, but it's not free.