postfix tuning debian 7

Add to all emails accounts on the server: ( i think the amounth is not important should exist something to apply on all emails from domain at once) DKIM Domainkey Spf filter this should work later on new addet emails and domain automatic. check postfix config for errors and open relay actualy spammers are using randowm_names(A)[login to view URL] to send spam we need prevent this by checking dkim, domainkey and spf