Answer
A Whitelist is a list of e-mail addresses or domain names from which an e-mail blocking program will allow messages to be received. For example, by including the domain "@umbc.edu" in your email's Whitelist, all messages that come from addresses "@umbc.edu" will pass through the email program's spam filtering system. If the Whitelist only contained a specific address from this domain, such as "email@umbc.edu," only messages from the sender "email@umbc.edu" would be certain to pass through. A Whitelist is often used to compensate for a spam-filtering system that is inadvertently identifying legitimate emails as spam.