excerpted from: https://www.campaignmonitor.com/
"Whitelisting" is a quick, one-time-only task to ensure the sender of an email gets added to the recipient’s address book or safe senders list.
To "whitelist" an email address just means you add them to your approved senders list. This tells your email client that you know this sender and trust them, which will keep emails from this contact at the top of your inbox and out of the junk folder.
For instructions on whitelisting our address,
'firstname.lastname@example.org' with YOUR email provider use this handy list of links: