qmail toaster: 554 mail server permanently rejected message (#5.3.0)

[Eric "Shubes"]

I've recently installed the qmail toaster (http://www.qmailtoaster.com) 
on CentOS. I'm in the process of redirecting messages from the old 
(hosted) server to my new one, and occasionally get the subject message.

Most messages come through ok, but several have been rejected. The 
rejected ones originated from various lists (including this one), and 
don't appear (to me) to be spam. They passed through a tighter 
spamassassin filter on the old server.

I'm new to this email server stuff, and don't know where to turn. I've 
googled the error, and it appears that qmail (or spamassassin or clamav) 
thinks there's something wrong with them. I've grep'd various logs, and 
haven't noticed anything indicative. I posted a message on the 
qmailtoaster list, but haven't heard back (yet), so I thought I'd try 
here, knowing that there's an abundance of talent here. I'm just looking 
for pointers.

TIA
-- 
-Eric 'shubes'