[Matt Hersant]

I'm having problems with spam for users who forge the sender to appear as one 
of my domains.  The spam is coming from an external mail server.  Is there 
anything I can add to my main.cf to combat this?  Any suggestions are 
appreciated.

smtpd_recipient_restrictions = 
    # allow password auth
    permit_sasl_authenticated,

    # allow local mail
    permit_mynetworks,

    # ease load on greylisting: drop wrong domains...
    reject_unauth_destination,

    # reject forged senders
    reject_non_fqdn_sender,

    # reject fake local senders
    #check_sender_access /etc/postfix/local_host_names

    # allow mtas from the DNS whitelist
    # This seems to be allowing spam.  Disabling for now.
    #check_client_access cidr:/etc/postfix/dnswl-header,
    #check_client_access cidr:/etc/postfix/dnswl-permit,

    # check black-/whitelist
    check_recipient_access hash:/etc/postfix/recv_access,

    # check black-/whitelist
    check_client_access hash:/etc/postfix/client_access,

    # check RBL
    reject_rbl_client sbl-xbl.spamhaus.org,

    # check RBL aparently dead
    #reject_rbl_client list.dsbl.org,

    # reject nonexisting domains
    reject_unknown_sender_domain,

    # reject domains without existing MX record
    # Need to figure out how to white list this.
    ####reject_rhsbl_sender bogusmx.rfc-ignorant.org,

    # drop unknown users BEFORE greylisting check
    reject_unlisted_recipient,

    ### THIS is the GREYLISTING activation
    check_policy_service inet:127.0.0.1:2525


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