Postfix Configuration Module

-Reject MTA software that doesn't send HELO (or EHLO) command at the beginning of an SMTP session to stop UEC, Unsolicited commercial e-mail, software.
<smtpd_helo_required>

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sender's restriction
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-Reject mail that does not have a return address( most spam does not have return address).
<reject_unknown_address>

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recipient's restriction
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-Permit the request when the client is successfully authenticated via the RFC 4954 (AUTH) protocol.
<permit_sasl_authenticated>

-Reject mail which doesn't have a valid to and from domain
<reject_non_fqdn_sender, reject_non_fqdn_recipient>

-Reject pipelinging and other than local destinations by unautorized users:
<reject_unauth_pipelining>
<reject_unauth_destination>

-Reject the request when the client HELO or EHLO parameter has a bad hostname syntax
<reject_invalid_hostname>

-Reject mail where there is no known sender or reciever domain
<reject_unknown_sender_domain, reject_unknown_recipient_domain>

-Reject the request when the hostname in the client HELO (EHLO) command is not in fully-qualified domain form
<reject_non_fqdn_hostname >

-Permit the request when the client IP address matches any network listed in $mynetworks.
<permit_mynetworks>

-a List of external BL
    reject_rbl_client relays.ordb.org,
    reject_rbl_client blackholes.easynet.nl,
    reject_rbl_client cbl.abuseat.org,
    reject_rbl_client proxies.blackholes.wirehub.net,
    reject_rbl_client bl.spamcop.net,
    reject_rbl_client sbl.spamhaus.org,
    reject_rbl_client opm.blitzed.org,
    reject_rbl_client dnsbl.njabl.org,
    reject_rbl_client list.dsbl.org,
    reject_rbl_client multihop.dsbl.org,