Yet Another Mail Merge lets you send your mail merge to one or more Google groups. Read this article for more details.
How to send a mail merge to a Google group?
List your Google groups row by row in your spreadsheet (and some optional information like their names etc.), just like any other email addresses.
Then click Send emails.
How is my campaign tracked?
Every time a group member opens the email, YAMM automatically records it as EMAIL_OPENED.
How will my quota be deducted?
Sending an email to one Google group reduces your quota by 1, regardless of the number of people in the group.