This article explains how to use an "undisclosed recipients" group and BCC to send an email to a group of people without exposing their names and email addresses to each other. These instructions apply to the web version of Yahoo Mail on any browser and any platform.

First, create an address book entry for 'unknown recipients' in Yahoo Mail:

Select the Contacts icon in the top right corner of Yahoo Mail (to the right of Sort) to open your address book.

Select New Contact from the left panel.