Make sure your smtp log is set to Detailed. Then check one of the messages. The line should look like this.
Mail rejected due to SMTP Spam Blocking: Barracuda, Protected Sky - Red, SORBS 06 - RECENT, SPAMHAUS - PBL 2, SPAMHAUS - XBL 1
This will give you a List of the Tests that Failed.
Junk Email filtered ISP