Whitelisting is a list in the cyber security which consist of the ip and domain who are trusted and are listed for sending spam free mails. They are present in the whitelist by having good past transactions, good ip reputation and many more factors.
It can be said that the ips and domains which are not in whitelist are present in the blacklist where they are marked as a malicious ip which have a reputation of sending virus and spam to their recipients .
It contains all the ips which are trusted to send good content to there recipients. When emails are send from these ips, they are more likely to land in inbox folder of the mail server.
It contains all the domains which are trusted to send good content to their recipients. When emails are sent from these domains, they are more likely to land in the inbox folder of the mail server.
All the email filter tools use this whitelist to filter there email , by using ip and domain whitelist they can find which ips are trusted to send good content rather than phishing mails to there recipients.
When ips are blacklisted for sending spoofing mails to their clients then they end up in the blacklist. However, there is also a chance to make them appear in the whitelist.
You can use some online tools to make your ip and domain whitelist but they will be delisted only if they observe that there is no malicious activity done from them and neither in the future such cases will be seen.