They had plenty of warning, their businesses have been prohibited by Mailchimp since at least early 2018. Expecting a company to give notice before enforcing its long-established policy is not realistic.

   > Some industries have higher-than-average abuse complaints, which can jeopardize the deliverability of our entire system. Nothing personal, but in order to maintain the highest delivery rates possible for all our customers, we can’t allow businesses that offer these types of services, products, or content:
  > 
  >[...]
  >
  > Also, we cannot allow businesses involved in any aspect of the sale, transaction, exchange, storage, marketing or production of cryptocurrencies, virtual currencies, and any digital assets related to an Initial Coin Offering, to use MailChimp to facilitate or support any of those activities.

https://web.archive.org/web/20180403195541/https://mailchimp...