What, you're not interested in a fabulous finger workout that comes from typing 1,500 emails in by hand? Good thing we can help.
From your Sign Ups page, click on the Groups icon to access the My Groups page. Click the pencil icon next to your group and select the option to Add Members. If you are in the Messages area composing a message, you can click Select People and select the option to Import emails from my provider.
If your contacts are not stored in one of those listed options, you can export your contacts to a CSV file and use that option to upload instead.