Postfix cant send mail: 450 4.7.1

I run postfix on Debian 4.? I have recently begun to receive non-deliverable errors when sending messages to freelists.org.? The error is 450 4.7.1.? I need this corrected.? I have full access to my DNS entries. ## Deliverables I am running postfix using unix accounts for mail on Debian 4.? I have recently begun receiving the following error when trying to send mail to freelists.org.? I have full control over my DNS records.? I have 3 domains pointing at one postfix server. Requirements: 1. Tell me how to change my postfix config / DNS records, without requiring another IP address, to fix this problem. This is the mail system at host zufelt.ca. I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below. For further assistance, please send mail to postmaster. If you do so, please include this problem report. You can delete your own text from the attached returned message. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? The mail system <<jfw@[login to view URL]>>: host [login to view URL][[login to view URL]] said: 450 4.7.1 ? ? ? Client host rejected: cannot find your hostname, [[login to view URL]] (in reply ? ? ? to RCPT TO command)