Sign in to your account at Yahoo! Mail and do the following:
Add the address to your contacts
Add the email address that is sending you an email (eg hello@example.com) to your Yahoo! Mail Contacts by clicking on the contacts icon:
And clicking Add a new contact:
Create a filter for the address
- Mouse over the Settings menu icon and select Settings
- Click Filters and then Add
- Enter a filter name
- Enter the domain of the email you want to whitelist in the Sender field, or
- Select Inbox as the folder to deliver the email to
- Click Save and then click Save again
