Allow listing (some services use the term, "whitelisting") refers to the process of granting a specific IP address access to a server or system. SendGrid's IP Access Management is one example of allow listing. IP Access Management is a security feature that allows you to control who can access your SendGrid account based on their IP address.
You may also hear the term allow list when referring to a list of IP addresses that receive special treatment when sending mail to a specific inbox provider. Email allow lists are becoming less and less common. These days, the best way to ensure your messages land in the inbox is to send mail that you know your recipients will love.
For more information on deliverability best practices, please visit our Deliverability Overview