I just POP'd my myrealbox.com account. I received 384 messages (100% spam), but your box only caught 51 messages.In the spamassassin setup, each email is given a score point and based on the score it will flag the email as spam or not. Our default setting for the score point is 5.
Here are some test results:
1) at default score point = 5, RF850 detected 43 SPAM mails out of 439
2) at score point = 2, RF850 detected 178 SPAM mails out of 439
3) at score point = 0, RF850 detected 416 SPAM mails out of 439
The lower the score point, the more SPAM mail will be detected, but the draw back is that some of the SPAM could be legitimate email.
To adjust the score point, you will need to manually edit a file /etc/mail/spamassassin/pop3/local.cf in the RF850 and adjust the value in statement "required_hits 5", change the value 5 to a lower value.