This addon will help you create an email template. You just need to replace the object by name of a column in Google Sheet. For example, the Google Sheet file has Email column, so in the template, it should be {Email}

What's new in Version 12?
Important change:
- (Apperance) Replace sidebar by dialog

New features:
- Setting menu
- Option to show/hide Toolbar type, Sender's name, and Attachment
- Confirmation box when hit SEND button
- Import email address manually