We're big fans of Kit (aff link) here at Teachery and that's why they're one of the few email providers we have direct integrations with.
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 Kit area
Enter your Kit API Key and click Save
You're integrated! 
Here's a video to walk you through our Kit integration and how you can use it within your Payment and Landing Pages:
Recommendation: Create individual Kit Forms for Teachery Payment or Landing PagesWe recommend that you create new Kit Forms for each Teachery Payment or Landing Page. This way, you can track exactly what's happening between Kit and Teachery, plus you can set up some fun automations in Kit with your course.
Every Payment or Landing Page lets you choose which Kit form you want to send data through to (they can all go to separate Kit Forms!)

Example Follow-Up Email Sequence If you want to send a new customer an email sequence after purchasing your course, you can easily create the sequence of emails in Kit and connect it to Teachery.
Create a new Sequence in Kit
Write your sequence emails and set the dates you want them to send (after the purchase happens in Teachery)
Publish your sequence so it's live and ready to send
Create a new Automation (Add Rule) in Kit
Create a trigger for when someone Subscribes to a Form they automatically Subscribe to a Sequence
You're all done in Kit! 
Edit the Payment Page customers will buy from
Click the Connect Email Provider button in the Actions menu
Select the specific Kit Form and click Save
You're all done in Teachery and your email sequence is ready for customers 
You can test this automation by purchasing your own course through your Teachery payment page that has the correct Kit form added to it (the one you just picked in the automation steps above). If you get the first email in the Kit Sequence, you're good to go!
Learn a ton more about Kit's automations here.