To send bulk email in HTML format, you need a plugin. Here is how to setup one of the more popular ones.
Add the plugin SMTPit_OSX to the FileMaker Extensions folder.
This plugin can be downloaded from www.smtpit.com
Make sure you get the version that works with FileMaker 6
Restart FileMaker and check under the FileMaker Pro menu, Preferences, Application menu item.
Click to see if the SMTPit plugin shows up. For now, we will ignore the Configure button below, as we will set this information from within FileMaker.