Filters automatically sort your incoming messages into folders that you create using the Yahoo! interface. They work according to rules that you set up — for example, you can create a filter that automatically delivers messages from your family members to a personal folder called "Family." Filters can save you time, since you don't need to read through each message to decide where it goes.
All Business Email owners may create up to 50 filters. To create, edit, or delete a filter:
Sign in to your account at http://mail.yourdomain.com/ (be sure to replace "yourdomain.com" with your domain name). You'll be prompted to enter your Yahoo! ID and password if you haven't already.
Click "Options" in the upper-right corner of the page, then choose "Mail Options" from the pull-down menu.

On the page that opens, select "Filters."

On the Filters page, click the "Create or edit filters" link.
The original Mail Filters page opens in a new window or tab.
Click the "Add" button.

The Add Message Filter page appears. This is where you define the rule and the destination for the new filter.
Enter a unique name for the new filter in the "Filter Name"box, such as "From Mom" or "Company Picnic."

If you don't enter a name, we'll automatically create a name for the filter when it adds it to your filter list.
Define the condition or conditions for the filter's rule. For each condition, you must specify the following:

From the "Move the message to" pull-down list, choose the destination folder to which you want the message delivered.

If you want the filter to direct messages to a new folder, select "[New Folder\" from the pull-down menu. When Yahoo! Business Email adds the new filter (that is, after you click the "Add Filter" button), it prompts you for a name and creates the new folder.
If you have configured your mobile device for alerts and would like to send an alert to your mobile device when this filter is activated, check the box next to "Send an alert to my Mobile Device."

Click the "Add Filter" button to save the filter.
The new filter appears in the list of filters on your Filters page and the total number of filters increases by one.

When you're done editing this filter, we recommend closing this window (your new Business Email interface is still open in another window or tab).
Ordering Your Filters
If you have more than one filter, you'll see "up" and "down" arrows to the right of the list of filters on the Filters page. Use these buttons to select the placement of your new filter within your existing sequence of filters.
Why is filter order important? It determines which filter is applied first. For example, Filter 1 will be the first filter applied to an incoming message, Filter 2 will be the next, and so on, until a match is made or all filters have been applied. If no filters match an incoming message, it will be delivered to your inbox.