To integrate Google Sheets, you need to get "JSON Auth" and "Spreadsheet ID" information.
+ Click Enable API and Services
+ Scroll down and click on Google Sheets API
+ Click Enable the Google Sheets API
+ Go to Credentials, then click Create credentials, and select Service account key.
+ Fill all the fields in Service account details form with 3 steps
+ For Key type, choose JSON (the default) and download the file. This file contains a private key so be very careful with it, it is your credentials after all.
Edit the sharing permissions to "Edit" for the spreadsheet you want to access to the client email address you can find in the JSON file.
+ Copy all content in JSON file and paste to JSON Auth field.
Create new Spreadsheet, where you want to send emails to. You can get spreadsheet ID from URL of this spreadsheet file like image below:
+ Open "Service accounts" and copy the email of the service account that you just created.
+ Go to the Spreadsheet to share the permission to that email:
Range that emails will insert into the spreadsheet. Example for A1:A9