I like GMail better than Yahoo.
Pashuteh Yid: you can probably allow http://mail.yahoo.com without allowing the entire yahoo.com but I still don’t like that site because the main page will have links to the main page with pictures and sometimes inappropriate headlines, etc. I would set them up with GMail accounts. The only problem you might have with GMail is the RSS feed on the top which can be edited in the settings. You can get rid of ads using AdBlockPlus for Firefox