WhiteList a legit e-mail address
If you have a legit user that is being caught by the spam filter or a customer that you want to make sure never gets caught...Login to http://login.postini.com
Click on "My Settings"
Click on "Approve Senders"
Enter the e-mail under "Approved Senders"
Be careful with the Approved Domains and Approved Mailing Lists options, doing so can open you up for more spam and virus activity. Especially if the address in question is being blocked due to legit spam activity.
The same process can be used to block addresses, but select block senders, instead of approve senders.