>>перво наперво убрать внешний адрес из mynetworks
>Так так убрал, теперь надо посмотреть и подождать день придет спам или
>нет. Дальше что нужно делать? Спасибо!

поставь greylisting (postgrey например)

smtpd_recipient_restrictions = permit_mynetworks,
                                reject_unauth_destination,                                  
                                reject_invalid_hostname,
                                reject_non_fqdn_hostname,
                                reject_non_fqdn_sender,
                                reject_non_fqdn_recipient,
                                reject_unknown_sender_domain,
                                reject_unknown_recipient_domain,
                                reject_unauth_pipelining,
                                reject_rbl_client bl.spamcop.net, --- это список спамеров
                                reject_rbl_client dnsbl.njabl.org,
                                reject_rbl_client sbl-xbl.spamhaus.org,
                                reject_rbl_client dul.dnsbl.sorbs.net,
                                reject_rbl_client smtp.dnsbl.sorbs.net,
                                reject_rbl_client socks.dnsbl.sorbs.net,
                                reject_rbl_client http.dnsbl.sorbs.net,
                                reject_rbl_client list.dsbl.org,
                                reject_rbl_client cbl.abuseat.org,
                                check_policy_service inet:127.0.0.1:60000 --- это тот самый postgrey
незабудь поставить кэширующий dns сервер