The steps to whitelist an email address can vary depending on the email client. Here are general guidelines for some popular email services:
Gmail
Open an email from the sender you want to whitelist. Click on the three vertical dots in the top-right corner of the email. Select "Add [Sender] to Contacts list."
Outlook
Open an email from the sender you want to whitelist. Right-click on the sender's email address. Select "Add to Safe Senders list."
Yahoo Mail
Open an email from the sender you want to whitelist. Click on the three horizontal dots in the top-right corner of the email. Select "Add Sender to Contacts."