To disable clamav, comment out the clamav sections for clamd and clamav in the amavisd configuration, e.g. on debian Linux the file is /etc/amavis/conf.d/15-av_scanners
add a # in front of these lines:
...
###
http://www.clamav.net/
['ClamAV-clamd',
\&ask_daemon, ["CONTSCAN {}\n", "/var/run/clamav/clamd.ctl"],
qr/\bOK$/, qr/\bFOUND$/,
qr/^.*?: (?!Infected Archive)(.*) FOUND$/ ],
....
and
....
###
http://www.clamav.net/ - backs up clamd or Mail::ClamAV
['ClamAV-clamscan', 'clamscan',
"--stdout --disable-summary -r --tempdir=$TEMPBASE {}",
[0], qr/:.*\sFOUND$/, qr/^.*?: (?!Infected Archive)(.*) FOUND$/ ],
.....
then restart amavisd.