It is the name given to the list containing e-mail or IP addresses defined as “Safe Sender” by the Internet service providers, e-mail users or e-mail service providers.

In other words, before an e-mail is delivered to you, the content of that e-mail is examined by the mail client and searched for signs of spam. If there is no indication that the e-mail is a spam, this sender is defined as a safe sender and the e-mail drops directly into the inbox. Messages received from a white-listed e-mail address do not drop into the spam box, but are sent directly to the recipient.