Create a Gmail Draft™ and Google Docs™ (if you want to include attachments) and use dynamic variables.
Create a datasheet in Google sheet and configure Simple Mail to send configured autometed emails.
Steps to use Simple Mail Merge:
1. Create a draft email in Gmail™. Use variables for keywords you want to be replaced dynamically. Use {{ variable }} to distinguish a variable.
2. (Optional) Create a Google Doc™ that you want to include as an attachment with the email. The attachment is sent as a PDF in the mail. Use variables for keywords you want to be replaced dynamically. Use {{ variable }} to distinguish a variable.
3. Create the Data sheet in Google sheets™ with columns same as the variable names. Configure the Simple Mail merge add and send email to your clients.