Automated welcome E-mail with App store

[pharaone37]

Dear Community, 

We built an app for the Shopify App Store and just wanting to be able to have an automatic email go out to those who purchase the app after they have purchased it. 

1- The App is already live and been approved by Shopify.

2–We want to set up an autoresponder, so each buyer gets a welcome message with installation guide 

Does anyone know the best option for this? 

Thanks in advance!