Note: There are two links provided for every major email platform. The first link takes you to that email platforms' instructions for whitelisting an email address, it is created, maintained, and updated by the email platform. The second link is from a 3rd party website that specializes in helping users whitelist an email address. The 3rd party website may provide addition insight, or workarounds to whitelist an email address, that may not be provided by the email platform.
Gmail
Outlook
Yahoo
iCloud
Comcast
Mail.com
AOL
...