Even if you choose to stay signed in when you sign in to Yahoo, Yahoo may still prompt you to sign in each time you check your Yahoo Mail. If this is the case, your browser will not store login cookies, which are bits of data that tell Yahoo that you are a returning visitor. To stay signed in to your Yahoo Mail account, you will need to make some adjustments to your browser's security settings.

The cookie that a browser stores when you visit Yahoo Mail applies only to the browser and device you were using at the time of your visit. As long as you visit the login page using the same device and browser, you will not need to log in again. However, if you log in using a different device or browser, Yahoo will not find the login cookie, so you will need to enter your username and password.

If you are using the same device and browser but are prompted to sign in, the cookie in the browser you use to sign in to Yahoo Mail has been automatically deleted.

There are several ways you can prevent your computer from deleting browser cookies, including the cookies for your Yahoo Mail login information.