If you use Gmail use these instructions.
- “Click the gear icon in Gmail and select “See all settings” from the Quick settings menu.
- Navigate to “Filters and Blocked Addresses” in the top menu.
- Select “Create a new filter.”
- Add a specific email or a whole domain in the “From” field.
- Click “Create filter.”
- Check “Never send it to Spam” in the checkbox.
- Click “Create filter.”
- https://blog.hubspot.com/marketing/email-whitelist
If you use Outlook.
- Click the gear icon in Outlook and select “View all Outlook settings.”
- Select “Mail” from the settings menu.
- Choose “Junk email” from the submenu.
- Click “Add” under “Safe senders and domains.”
- Enter the email address that you want whitelisted.
- Choose “Save.”
- https://blog.hubspot.com/marketing/email-whitelist
If you use Yahoo.
- Open Yahoo Mail and log into your account.
- Navigate to “Settings” then click “More Settings.”
- Select “Filters” and hit “Add” to enter the email you’d like to whitelist.
- Name the filter and add the email address.
- Select to send all mail to “Inbox.”Save your settings.”
- https://blog.hubspot.com/marketing/email-whitelist