I was looking high and low for a good Mac mail merge and found it

SerialMailer seems exactly perfect for what I wanted to do.

I tried mail merge in Word, but it requires I use Entourage (Word 2008) or Outlook (Word 2011) as my default mail app, and I wanted to use Apple Mail.

I tried the mail merge in FileMaker, but it only supports plain text, you have to awkwardly compose mails as "calculated fields," there is no preview and no watching the progress of sent emails. Basically, FileMaker is awkward to use for mail merge.

But with SerialMailer I can compose emails in a normal looking, if simple, editor, I can preview each message before it goes out, I can choose to use formatted emails (works fine), there are "smart fields" which depend on the values of the fields I import from FMP, I can easily save and re-use templates, and I can even track the progress as the mails are sent out. And all my test emails arrived just fine.

Its really everything I was looking for in a mail merge. I will be purchasing the paid version.

In Situ about SerialMailer Lite