Too Long; Didn't Read
There are 2 ways to mail merge in Gmail. You can either use a Google add-on that will do the job for you or build your own mail merge script. We recommend using software built for that purpose which cover most issues and will probably save you time. Using Mailmeteor is a tool that integrates with Gmail and Google Sheets to merge emails with Gmail. We're going to use Google Apps Script, which makes it really easy to create add-ons. The script we are using has been created and proofread by Google Apps script teams.