No spam filter is 100% accurate all the time. For that reason, Pobox Spam Protection includes two methods of creating trusted senders automatically (whitelisting), which exempts certain email addresses from spam processing.
If one of your legitimate messages is caught by the Spam Protection system, just release the message to your forwarding address, and the person who sent that message can be made a trusted sender right away. On the next page, you can choose "Add As Trusted Sender" or "Do Not Add As Trusted Sender" (as well as showing you any other messages we've held from that email address.) Just select the option you want, and click "Release Checked + Delete Others" again.
You can also make every person you send mail to a trusted sender by using Pobox to send your outgoing mail. Get instructions on sending your outgoing mail through Pobox.