Clamav got fed up with users of version 0.94 downloading updates from them and not supporting signatures greater than 980 bytes, so they pushed an update that broke clamav 0.94, causing it to reject all email. At the time clamav0.94 was just over a year old, and was the version found in debian stable.
add to /etc/apt.sources.lists deb http://www.backports.org/debian etch-backports main contrib non-free or deb http://www.backports.org/debian lenny-backports main contrib non-free apt-get update apt-get install libclamav6 wget http://www.backports.org/debian/pool/main/c/clamav/clamav_0.95.2+dfsg-2~bpo40+1_i386.deb wget http://www.backports.org/debian/pool/main/c/clamav/clamav-daemon_0.95.2+dfsg-2~bpo40+1_i386.deb wget http://www.backports.org/debian/pool/main/c/clamav/clamav-base_0.95.2+dfsg-2~bpo40+1_all.deb wget http://www.backports.org/debian/pool/main/c/clamav/clamav-freshclam_0.95.2+dfsg-2~bpo40+1_i386.deb dpkg -i clamav-daemon_0.95.2+dfsg-2~bpo40+1_i386.deb clamav-base_0.95.2+dfsg-2~bpo40+1_all.deb clamav-freshclam_0.95.2+dfsg-2~bpo40+1_i386.deb