Google Message Security for Google Apps Administration Guide - Manual (Page 257)

Approved and Blocked Sender Lists 257
Approved Domains
Messages from an approved domain are delivered to user inboxes, regardless of
spam-like content. Messages from approved domains always circumvent junk
email filters. However, if virus blocking is enabled for the recipient, the message
security service does not deliver a message containing a virus, even if the domain
is approved.
Approved senders can optionally override Attachment Manager and Content
Manager filtering.
Approved Mailing/Email Lists
Messages sent to an approved mailing/email list are delivered to user inboxes,
regardless of spam-like content. Messages from approved mailing lists always
circumvent junk email filters. However, if virus blocking is enabled for the
recipient, the email security service does not deliver a message containing a
virus, even if the mailing/email list is approved.
Approved senders can optionally override Attachment Manager and Content
Manager filtering.
Many mailing/email-list and newsgroup emails contain characteristics in common
with spam. In fact, one person's opt-in mailing/email list can be perceived by
another person as spam.
If you find mailing/email-list or newsgroup postings quarantined in the Message
Center, add that list to the approved mailing/mail list to prevent the messages
from being quarantined
The Approved Mailing list evaluates the “To” and “Cc” fields on each message —
a mailing/email list most often place its address in those fields rather than the
“From” field.
Never add yourself to your own Approved Mailing list. Since the Approved Mailing
list is based on the recipient of the email, this causes all mail to bypass filtering.
Blocked Senders
Messages from individual senders or entire domains are quarantined, regardless
of content.
You can add specific senders, for example, who otherwise keep getting past your
other filters. (This feature works only if spam filtering is turned ON.)
Blocked Domains
Messages from an entire domain are quarantined, regardless of content.