(1) A list of "from" e-mail addresses that a mail server is configured to accept as incoming mail. E-mail filtering that relies entirely on white lists is severely restricted because only messages from addresses on the list are allowed, and all the rest are discarded. See spam filter. Contrast with blacklist.

(2) A list of valid domain names that a mail server is configured to accept. All mail from users with that domain are allowed. Contrast with blacklist.

(3) A list of Web sites that are allowed to be accessed. A company can configure its routers and firewalls to allow only certain Web sites to be accessed because they relate to business. Contrast with blacklist.