[exim] quota

Hello,

I've just discovered, the "0" disables quota instead of what I've
believed to not allow any mail through. If "0" essentially removes
all restriction on quota, what is the opposite? How do you limit it
to no mail?

   quota = ${lookup mysql{select users.quota from users,domains \
           where localpart = '${quote_mysql:$local_part}' \
        and domain = '${quote_mysql:$domain}' \
        and users.domain_id = domains.domain_id}{${value}M}}
   quota_is_inclusive = false
   quota_size_regex = ,S=(\d+):
   quota_warn_threshold = 75%
   maildir_use_size_file = false

Thanks,

George