If you send emails to groups of people using Gmail, you owe it to yourself to visit the GMass website. Once you understand what their product does, I think you’re going to love it.

Send email campaigns to your existing Gmail contacts. Personalize based on name and email address. Schedule mass emails to be sent later. Track opens. Create instant recipient lists based on search results. And the killer feature – emails can be sent as replies to the last conversation you had with each recipient.

Source: GMass – a beautiful mass email and mail merge tool for Gmail