Yes. When you sign into your Yahoo! Webmail account, a cookie is set in your browser for identification and authentication. When you visit Yahoo!, our servers recognize that the cookie belongs to your account. If the cookie has expired or been deleted, that browser cannot be used to view your mail, and you will be prompted to reenter your password or sign in again. Some Yahoo! services require a more recent cookie, and others will accept the cookie as long as it has not expired.
To prevent someone else from using the "Back" button or the History function to access your email account, it's a good idea to take some precautions when you're finished using your account, particularly if you use a public or shared computer. Be sure to sign out of your email account, clear the browser's cache, and close your browser so the next person using the computer will be returned to the log-in screen — not your account — if trying to view the browser history.
To sign out:Click the Welcome Message link (for example, "Hi, Mary") or the image next to it.
Business Email Welcome Message
Welcome Menu: Sign Out
Previous Business Email Sign-Out Link
Yahoo! Home Page Sign-Out Link
Yahoo! Account Info Page Sign-Out Link
Remember: if you don't sign out, it may be possible for someone else using the same computer to access your account if they return to Yahoo! before the login session expires.