Add file:
/etc/amavis/conf.d/90-custom

with this content:

Code:
use strict;

#
# Place your configuration directives here. They will override those in
# earlier files.
#
# See /usr/share/doc/amavisd-new/ for documentation and examples of
# the directives you can use in this file
#

$max_servers = 1;

#------------ Do not modify anything below this line -------------
1; # insure a defined return
and then restart amavis.

in postfix master.cf, change the line:

amavis unix - - - - 2 smtp

to:

amavis unix - - - - 1 smtp

and restart postfix.