EasyMerge

Mail merge, minus the mail merge. Write your email the way you always do, with everyone in the To field. Type your own wildcards directly in the email: _FIRST_NAME, _COMPANY, _ETC. Anything in all caps that starts with an underscore is a wildcard. When you hit Send, EasyMerge shows a row for each recipient, fills in what it can, and asks you for the rest. Then each person gets their own email, attachments included. That's it. Really. Want to send it again later? Open a new message and click the EasyMerge button in the compose toolbar. Your last EasyMerge email comes back with its wildcards intact. Private by design. Everything happens in your Gmail tab. EasyMerge has no server and never sends your email content anywhere.