Clue is to have a look in you /var/log/qpsmtpd/current and see why it was denied.
Here's a suspicious couple of lines from that logfile:
2007-08-29 07:23:21.790748500 5961 spooling message to disk
2007-08-29 07:23:21.939044500 5961 virus::clamav plugin: Changing permissions on file to permit scanner access
2007-08-29 07:23:21.947326500 5961 virus::clamav plugin: clamscan results: connect(): No such file or directory
2007-08-29 07:23:21.947333500 WARNING: Can't connect to clamd.
2007-08-29 07:23:21.948134500 5961 virus::clamav plugin: ClamAV error: /usr/bin/clamdscan --stdout --config-file=/etc/clamd.conf --disable-summary /var/spool/qpsmtpd/1188390201:5961:0 2>&1: 2
2007-08-29 07:23:21.948143500
2007-08-29 07:23:21.951329500 5961 logging::logterse plugin: ` 127.0.0.1 localhost localhost <user@smeserv.org> <user@domain.com> virus::clamav 902 msg denied before queued
2007-08-29 07:23:21.953202500 5961 452 Message denied temporarily