try this
edit: /opt/zimbra/conf/amavisd.conf.in
line 24
from
%%uncomment VAR:zimbraDomainMandatoryMailSignatureEnabled%%@al termime_args_disclaimer = qw(--verbose --disclaimer=/opt/zimbra/data/altermime/
_OPTION_.txt --disclaimer-html=/opt/zimbra/data/altermime/_OPTION_.html );
to
%%uncomment VAR:zimbraDomainMandatoryMailSignatureEnabled%%@al termime_args_disclaimer = qw(--verbose --disclaimer=/opt/zimbra/data/altermime/
xx.txt --disclaimer-html=/opt/zimbra/data/altermime/_OPTION_.html );
and
create file /opt/zimbra/data/altermime/xx.txt
and edit your disclaimer in that file (xx.txt)
restart zmamavisdctl

