GlassFrog allows you to email members of your circle by following these steps. The result is a list of email addresses for your circle members, each separated by a comma.
For Microsoft Outlook, however, the default email-address separator is a semicolon. If you would like to use the GlassFrog email feature, you have two options:
1) If you're using Windows, you can change your Outlook email to allow the use of a comma in addition to a semicolon. We found these instructions that walk you through how to do this for various versions of Outlook.
2) Or, you can use the steps to email all members (the same link as was provided above) and then edit the resulting email strings to replace the commas with semicolons.