Typically, we think of filters blocking things: a water filter keeps dirt out of the water. But some filters select and direct what passes through them, and this is the kind of filter Yahoo! Mail uses. Yahoo! Mail's filters automatically sort incoming messages into the folders you want, so that you don't need to read through each message to decide where it goes. A filter can also alert you of new email on your mobile device.
Filters function according to rules you set up. For example, you could create a filter to deliver messages from your family members automatically to a folder called "Family." Or, messages from coworkers could trigger a text alert on your mobile phone.
You can create up to 100 filters in your free Yahoo! Mail account. If you need more filters, check out Yahoo! Mail Plus which offers up to 200 filters.
To create, edit, or delete a filter, click Options > More Options in the upper-right corner of your Yahoo! Mail page. From the list on the left, choose Filters. Click Create or Edit Filters.