1-2-3 Mail merge is a Google Spreadsheet add-on that sends mail based on a mail template which is merged with data from the Spreadsheet. The mail template is captured in the sheet as well.
 
Mail merge in 3 steps:
 - First, fill in the Data sheet with the personal data per row
 - Second, create your mail template, use HTML for the layout
 - Third step is to send the mail merge

You can easily check your mail quota, preview the mail text or send a preview message to yourself.