SpamAssassin Rule: USER_IN_DEF_WHITELIST
Standard description: From: address is in the default white-list
The From: address was listed in the default whitelist. The whitelist contains a series of addresses and domains that are allowed to relay for that address.
These should be addresses which send mail that is often tagged (incorrectly) as spam; it also helps that they be addresses of big companies with lots of lawyers, so if spammers impersonate them, they'll get into big trouble, so it doesn't provide a shortcut around SpamAssassin.
The default scores for this rule can be found in the online list of tests.