Exim4 won't send message
Directory permissions on /var/spool/exim4/scan should be 750, and owned by the exim user and its primary group (on my FreeBSD systems, these are mailnull and mail, respectively).
If your clamav user has Debian-exim as a supplementary group - that is, if Debian-exim is not its primary group, then you need "AllowSupplementaryGroups yes" in your clamd.conf (and clamd must be started by root).
I had the same problem on Centos 6.2 running exim4 with clamAV, solved it by adding clam user to the mail group.
# usermod -a -G mail clam