Скачать или смотреть How to use and send predefined Email Template as Mail

Create mail merge with Gmail and Google Sheets.This will help you to use predefined email template. You can do more by using Yet another mail merge support. see the description given below.
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YAMM is the most popular Google Sheets add-on for Gmail and G Suite users. It stays as a favorite add-on for its users and much regarded for its email deliverability to recipients’ inboxes and affordability.

This mail merge tool is a simple solution to send personalized emails and newsletters or notifications on forms submissions to multiple recipients.

YAMM is an easy-to-use Mail Merge tool for users unfamiliar with HTML:
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Select a draft written in Gmail
Replace variables/markers from your email template with names
and other information from the spreadsheet
Send automatically personalized emails to your contact list from
your spreadsheet