Here's the relevant text from the email :
What's new in the free plan?
With so many new channels to put to work for your business, our definition of “audience” is changing to include all of the contacts you can market to regardless of their email opt-in/subscriber status. So that happy customer that’s been on your subscriber list for 2 years? They’ll still be a part of your audience. But those customers that unsubscribed and that customer that attended your event but never opted in to your newsletter? They’ll be in your audience now too.
These new channels allow you to leverage your entire audience, so you can encourage new engagement with your brand. It’s much more expensive to find new customers than to keep existing ones, so be sure to market to the audience you’ve worked so hard to build.
What does this mean for you?
As we've grown beyond email to be an all-in-one Marketing Platform, we've created new plans to include all of our new features and capabilities. As a current user of our Forever Free plan, you'll now be in the new Free plan as long as your audience size is 2,000 contacts or less. The new pricing structure is based upon the total number of contacts you can market to, which now includes unsubscribes and customers who have simply not opted-in yet. You can check your Mailchimp account to see how many contacts are in your total audience. And keep in mind, you can always archive contacts you aren't using. On June 15, 2019, the pricing change will go into effect if you have more than 2,000 contacts.
Plus, if you’d like to upgrade to a paid plan and get access to all of the features in our new plans like removing Mailchimp branding, using retargeting ads, or getting access to 24x7 support, check out mailchimp.com tomorrow for all the new plans to see what best fits your needs.