Whitelisting - greylisting.org. Greylisting.Org > ADVERTISEMENTS When one does greylisting one generally also need to do some whitelisting.
Whitelisting basically means having a list of sender email servers (IPs) / sender email addresses that are never refused on first try (as greylisting does). In some cases you might do this because you trust the mailer and do not want to delay whatever mail it sends to you. Whitelisting - greylisting.org.