Depending on exactly what you need to do—whether you are (so you can receive their emails again) or unblocking emails stuck in the Spam folder —the steps differ slightly.
Here’s a short, story-based walkthrough for unblocking emails on Yahoo Mobile, written as if a friend is helping you out.
Under you can add or remove entire domains (e.g., @example.com) by tapping the X or Remove button. Troubleshooting: Still Not Receiving Emails?
If you are on your phone, follow these steps to access your blocked list: