One of the new features in Yahoo Mail is the contact manager. It’s similar to a paper or desktop address book but has a lot more features and functions such as categories and links to your connections.
Yahoo! Contacts is an online contact manager that helps you organize and communicate with the people in your life.

1. In Mail, click the Contacts link in the left pane.
2. While viewing your profile, click the Contacts tab.
3. The contacts page opens displaying all of your contacts.
4. From here, you can

a. Add contacts.
b. Connect with those closest to you.
c. Create categories so that you can organize your contacts.
d. Work with contact details.

You can learn more over here: http://overview.mail.yahoo.com/products/new

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