Google Message Security for Google Apps Administration Guide - Manual (Page 184)

184 Message Security for Google Apps Administration Guide
If so, all spam addressed to the user, regardless of any spam settings, is
delivered to that user’s inbox. Log in to the Message Center and remove that
user’s address or domain from this list. Then let the user know why adding
your own address or domain here is not a good idea.
6. Does the email content have enough spam characteristics to trigger
filtering?
In general, if all prior steps have turned out to be false, the spam did not have
sufficient spam characteristics to be filtered. Confirm this by checking the
message header for its spam score (see “ Interpreting Header Fields” on
page 401).
If you have further questions, please see the Help Center.
When Spam Still Gets Through
If you find that a large amount of spam is still slipping through the filters, follow the
steps below:
1. Add repeat spammers to the user- or org-level Blocked Senders list.
This may be effective for a short time, as long as the spammers do not
change their addresses.