Mailchimp is a great email service and here, at Teachery, we're happy to have a direct integration with them!
It couldn't be easier to connect your account!
Click Account in the top navigation of Teachery
Click the Integrations link option
Scroll down to find the Mailchimp area
Enter your Mailchimp API Key and click Save
You're integrated! 
Here's a video to walk you through our Mailchimp Integration and how you can use it within your Payment and Landing Pages.
Add customers to your Mailchimp account via our Payment or Landing PagesEvery Payment or Landing Page lets you choose to which List (now called Audience in Mailchimp) and then which Tag(s) (within that Audience) to assign a subscriber:
In the Actions menu, select Connect Email Provider and if you haven’t already, connect Mailchimp
Select your List (a.k.a Audience)
Then, select your Tag(s)
We recommend enabling double opt-in but make sure you’ve set this up in Mailchimp first (in your Audience settings)
You can create brand new Tags from within our integration but note that they may not appear in Mailchimp until your first subscriber joins.

Learn a ton more about Mailchimp's automations here.