dmarc: added relaxed alignment tests
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plugins/dmarc
166
plugins/dmarc
@ -40,16 +40,12 @@ See Section 10 of the draft: Domain Owner Actions
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pct=50; (percent of messages to filter)
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=head2
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=head1 DRAFT
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http://www.dmarc.org/draft-dmarc-base-00-02.txt
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=head1 TODO
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1. run dmarc before SPF, if DMARC policy is discovered, ignore SPF
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2. provide dmarc feedback to domains that request it
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3. If a message has multiple 'From' recipients, reject it
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@ -58,7 +54,7 @@ http://www.dmarc.org/draft-dmarc-base-00-02.txt
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=head1 IMPLEMENTATION
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1. Primary identifier is RFC5322.From field
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1. Primary identifier is RFC5322.From field (From: header)
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2. Senders can specify strict or relaxed mode
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@ -72,29 +68,6 @@ http://www.dmarc.org/draft-dmarc-base-00-02.txt
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RFC5322.From purports to be from a domain that appears to be
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either non-existent or incapable of receiving mail.
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=head2 Reports should include
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The report SHOULD include the following data:
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o Enough information for the report consumer to re-calculate DMARC
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disposition based on the published policy, message dispositon, and
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SPF, DKIM, and identifier alignment results. {R12}
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o Data for each sender subdomain separately from mail from the
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sender's organizational domain, even if no subdomain policy is
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applied. {R13}
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o Sending and receiving domains {R17}
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o The policy requested by the Domain Owner and the policy actually
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applied (if different) {R18}
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o The number of successful authentications {R19}
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o The counts of messages based on all messages received even if
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their delivery is ultimately blocked by other filtering agents
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{R20}
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=cut
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use strict;
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@ -123,15 +96,13 @@ sub data_post_handler {
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# 11.1. Extract Author Domain
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# TODO: check exists_in_dns result, and possibly reject here if domain non-exist
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my $from_host = $self->get_from_host($transaction) or return DECLINED;
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if (!$self->exists_in_dns($from_host)) {
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my $org_host = $self->get_organizational_domain($from_host);
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if (!$self->exists_in_dns($org_host)) {
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$self->log(LOGINFO, "fail, domain/org not in DNS");
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#return $self->get_reject();
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return DECLINED;
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if (!$self->exists_in_dns($from_host)) {
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if (!$self->exists_in_dns($org_host)) {
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$self->log(LOGINFO, "fail, $from_host not in DNS");
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return $self->get_reject("RFC5322.From host does not exist");
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}
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}
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@ -140,18 +111,30 @@ sub data_post_handler {
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or return DECLINED;
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# 3. Perform DKIM signature verification checks. A single email may
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# contain multiple DKIM signatures. The results of this step are
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# passed to the remainder of the algorithm and MUST include the
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# value of the "d=" tag from all DKIM signatures that successfully
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# validated.
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my $dkim_sigs = $self->connection->notes('dkim_pass_domains') || [];
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# contain multiple DKIM signatures. The results MUST include the
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# value of the "d=" tag from all DKIM signatures that validated.
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#my $dkim_sigs = $self->connection->notes('dkim_pass_domains') || [];
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# 4. Perform SPF validation checks. The results of this step are
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# passed to the remainder of the algorithm and MUST include the
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# domain name from the RFC5321.MailFrom if SPF evaluation returned
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# a "pass" result.
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# 4. Perform SPF validation checks. The results of this step
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# MUST include the domain name from the RFC5321.MailFrom if SPF
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# evaluation returned a "pass" result.
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my $spf_dom = $transaction->notes('spf_pass_host');
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# 5. Conduct identifier alignment checks.
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return DECLINED
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if $self->is_aligned($from_host, $org_host, $policy, $spf_dom );
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# 6. Apply policy. Emails that fail the DMARC mechanism check are
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# disposed of in accordance with the discovered DMARC policy of the
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# Domain Owner. See Section 6.2 for details.
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return DECLINED if lc $policy->{p} eq 'none';
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return $self->get_reject("failed DMARC policy");
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}
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sub is_aligned {
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my ($self, $from_host, $org_host, $policy, $spf_dom) = @_;
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# 5. Conduct identifier alignment checks. With authentication checks
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# and policy discovery performed, the Mail Receiver checks if
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# Authenticated Identifiers fall into alignment as decribed in
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@ -160,34 +143,43 @@ sub data_post_handler {
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# the DMARC mechanism check. All other conditions (authentication
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# failures, identifier mismatches) are considered to be DMARC
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# mechanism check failures.
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my $dkim_sigs = $self->connection->notes('dkim_pass_domains') || [];
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foreach (@$dkim_sigs) {
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if ($_ eq $from_host) { # strict alignment
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$self->log(LOGINFO, "pass, DKIM alignment");
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$self->adjust_karma(2); # big karma boost
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return DECLINED;
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$self->log(LOGINFO, "pass, DKIM aligned");
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$self->adjust_karma(1);
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return 1;
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}
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next if $policy->{adkim} && lc $policy->{adkim} eq 's'; # strict pol.
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# default policy is relaxed
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if ( $_ eq $org_host ) {
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$self->log(LOGINFO, "pass, DKIM aligned, relaxed");
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$self->adjust_karma(1);
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return 1;
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};
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}
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if ($spf_dom && $spf_dom eq $from_host) {
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$self->adjust_karma(2); # big karma boost
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$self->log(LOGINFO, "pass, SPF alignment");
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return DECLINED;
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return 0 if ! $spf_dom;
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if ($spf_dom eq $from_host) {
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$self->adjust_karma(1);
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$self->log(LOGINFO, "pass, SPF aligned");
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return 1;
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}
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return 0 if ($policy->{aspf} && lc $policy->{aspf} eq 's' ); # strict pol
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if ($spf_dom eq $org_host) {
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$self->adjust_karma(1);
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$self->log(LOGINFO, "pass, SPF aligned, relaxed");
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return 1;
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}
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# 6. Apply policy. Emails that fail the DMARC mechanism check are
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# disposed of in accordance with the discovered DMARC policy of the
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# Domain Owner. See Section 6.2 for details.
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$self->log(LOGINFO, "skip, NEED RELAXED alignment");
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return DECLINED;
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}
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return 0;
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};
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sub discover_policy {
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my ($self, $from_host) = @_;
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# 1. Mail Receivers MUST query the DNS for a DMARC TXT record at the
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# DNS domain matching the one found in the RFC5322.From domain in
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# the message. A possibly empty set of records is returned.
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# 1. Mail Receivers MUST query the DNS for a DMARC TXT record...
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my @matches = $self->fetch_dmarc_record($from_host); # 2. within
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if (0 == scalar @matches) {
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@ -304,29 +296,45 @@ sub get_organizational_domain {
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sub exists_in_dns {
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my ($self, $domain) = @_;
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# the DMARC draft suggests rejecting messages whose From: domain does not
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# exist in DNS. That's as far as it goes. So I went back to the ADSP (from
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# where DMARC this originated, which in turn led me to the ietf-dkim email
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# list where a handful of 'experts' failed to agree on The Right Way to
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# perform this test. And thus no direction was given.
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# As they point out:
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# MX records aren't mandatory.
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# A or AAAA records as fallback aren't reliable either.
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# I chose to query the name and match NS,MX,A,or AAAA records. Since it gets
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# repeated for the for the Organizational Name, if it fails, there's no
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# delegation from the TLD.
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my $res = $self->init_resolver();
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my $query = $res->send($domain, 'NS') or do {
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my $query = $res->send($domain) or do {
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if ($res->errorstring eq 'NXDOMAIN') {
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$self->log(LOGDEBUG, "fail, non-existent domain: $domain");
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return;
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}
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$self->log(LOGINFO,
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"error, looking up NS for $domain: " . $res->errorstring);
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$self->log(LOGINFO, "error, looking up $domain: " . $res->errorstring);
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return;
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};
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my @matches;
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for my $rr ($query->answer) {
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next if $rr->type ne 'NS';
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next if $rr->type !~ /(?:NS|MX|A|AAAA)/;
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push @matches, $rr->nsdname;
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}
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if (0 == scalar @matches) {
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$self->log(LOGDEBUG, "fail, zero NS for $domain");
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$self->log(LOGDEBUG, "fail, no records for $domain");
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}
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return @matches;
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}
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sub fetch_dmarc_record {
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my ($self, $zone) = @_;
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# 1. Mail Receivers MUST query the DNS for a DMARC TXT record at the
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# DNS domain matching the one found in the RFC5322.From domain in
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# the message. A possibly empty set of records is returned.
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my $res = $self->init_resolver();
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my $query = $res->send('_dmarc.' . $zone, 'TXT');
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my @matches;
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@ -366,6 +374,34 @@ sub parse_policy {
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return %dmarc;
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}
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sub external_report {
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=pod
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The report SHOULD include the following data:
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o Enough information for the report consumer to re-calculate DMARC
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disposition based on the published policy, message dispositon, and
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SPF, DKIM, and identifier alignment results. {R12}
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o Data for each sender subdomain separately from mail from the
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sender's organizational domain, even if no subdomain policy is
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applied. {R13}
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o Sending and receiving domains {R17}
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o The policy requested by the Domain Owner and the policy actually
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applied (if different) {R18}
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o The number of successful authentications {R19}
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o The counts of messages based on all messages received even if
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their delivery is ultimately blocked by other filtering agents {R20}
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=cut
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};
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sub verify_external_reporting {
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=head2 Verify External Destinations
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