347 lines
9.8 KiB
Perl
347 lines
9.8 KiB
Perl
#!perl -w
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=head1 NAME
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dnsbl - handle DNS BlackList lookups
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=head1 DESCRIPTION
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Plugin that checks the IP address of the incoming connection against
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a configurable set of RBL services.
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=cut
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sub register {
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my ($self, $qp) = shift, shift;
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if ( @_ % 2 ) {
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$self->{_args}{reject_type} = shift; # backwards compatibility
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}
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else {
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$self->{_args} = { @_ };
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};
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my $rej = $self->{_args}{reject_type};
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$self->{_dnsbl}{DENY} = (defined $rej && $rej =~ /^disconnect$/i) ? DENY_DISCONNECT : DENY;
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}
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sub hook_connect {
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my ($self, $transaction) = @_;
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# perform RBLSMTPD checks to mimic Dan Bernstein's rblsmtpd
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return DECLINED if $self->is_set_rblsmtpd();
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return DECLINED if $self->ip_whitelisted();
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my %dnsbl_zones = map { (split /:/, $_, 2)[0,1] } $self->qp->config('dnsbl_zones');
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if ( ! %dnsbl_zones ) {
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$self->log( LOGDEBUG, "skip: no list configured");
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return DECLINED;
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};
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my $remote_ip = $self->qp->connection->remote_ip;
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my $reversed_ip = join('.', reverse(split(/\./, $remote_ip)));
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# we queue these lookups in the background and fetch the
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# results in the first rcpt handler
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my $res = new Net::DNS::Resolver;
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$res->tcp_timeout(30);
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$res->udp_timeout(30);
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my $sel = IO::Select->new();
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my $dom;
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for my $dnsbl (keys %dnsbl_zones) {
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# fix to find A records, if the dnsbl_zones line has a second field 20/1/04 ++msp
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$dom->{"$reversed_ip.$dnsbl"} = 1;
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if (defined($dnsbl_zones{$dnsbl})) {
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$self->log(LOGDEBUG, "Checking $reversed_ip.$dnsbl for A record in the background");
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$sel->add($res->bgsend("$reversed_ip.$dnsbl"));
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}
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else {
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$self->log(LOGDEBUG, "Checking $reversed_ip.$dnsbl for TXT record in the background");
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$sel->add($res->bgsend("$reversed_ip.$dnsbl", "TXT"));
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}
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}
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$self->qp->connection->notes('dnsbl_sockets', $sel);
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$self->qp->connection->notes('dnsbl_domains', $dom);
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return DECLINED;
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}
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sub is_set_rblsmtpd {
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my $self = shift;
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my $remote_ip = $self->qp->connection->remote_ip;
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if ( ! defined $ENV{'RBLSMTPD'} ) {
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$self->log(LOGDEBUG, "RBLSMTPD not set for $remote_ip");
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return;
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};
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if ($ENV{'RBLSMTPD'} ne '') {
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$self->log(LOGINFO, "RBLSMTPD=\"$ENV{'RBLSMTPD'}\" for $remote_ip");
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return $ENV{'RBLSMTPD'};
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}
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$self->log(LOGINFO, "RBLSMTPD set, but empty for $remote_ip");
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return 1; # don't return empty string, it evaluates to false
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};
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sub ip_whitelisted {
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my ($self) = @_;
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my $remote_ip = $self->qp->connection->remote_ip;
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my $white = $self->qp->connection->notes('whitelisthost');
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if ( $white ) {
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$self->log(LOGDEBUG, "skip: whitelist overrode blacklist: $white");
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return 1;
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};
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if ( $self->qp->connection->relay_client() ) {
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$self->log(LOGWARN, "skip: don't blacklist relay/auth clients");
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return 1;
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};
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return grep { s/\.?$/./;
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$_ eq substr($remote_ip . '.', 0, length $_)
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}
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$self->qp->config('dnsbl_allow');
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};
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sub process_sockets {
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my ($self) = @_;
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my $conn = $self->qp->connection;
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return $conn->notes('dnsbl') if $conn->notes('dnsbl');
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my %dnsbl_zones = map { (split /:/, $_, 2)[0,1] } $self->qp->config('dnsbl_zones');
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my $sel = $conn->notes('dnsbl_sockets') or return '';
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my $dom = $conn->notes('dnsbl_domains');
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my $remote_ip = $self->qp->connection->remote_ip;
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my $result;
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my $res = new Net::DNS::Resolver;
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$res->tcp_timeout(30);
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$res->udp_timeout(30);
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$self->log(LOGDEBUG, "waiting for dnsbl dns");
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# don't wait more than 8 seconds here
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my @ready = $sel->can_read(8);
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$self->log(LOGDEBUG, "DONE waiting for dnsbl dns, got ", scalar @ready, " answers ...");
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return '' unless @ready;
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for my $socket (@ready) {
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my $query = $res->bgread($socket);
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$sel->remove($socket);
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undef $socket;
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my $dnsbl;
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if ($query) {
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my $a_record = 0;
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foreach my $rr ($query->answer) {
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my $name = $rr->name;
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$self->log(LOGDEBUG, "name $name");
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next unless $dom->{$name};
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$self->log(LOGDEBUG, "name $name was queried");
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$a_record = 1 if $rr->type eq "A";
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($dnsbl) = ($name =~ m/(?:\d+\.){4}(.*)/) unless $dnsbl;
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$dnsbl = $name unless $dnsbl;
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next unless $rr->type eq "TXT";
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$self->log(LOGDEBUG, "got txt record");
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$result = $rr->txtdata and last;
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}
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#$a_record and $result = "Blocked by $dnsbl";
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if ($a_record) {
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if (defined $dnsbl_zones{$dnsbl}) {
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$result = $dnsbl_zones{$dnsbl};
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#$result =~ s/%IP%/$ENV{'TCPREMOTEIP'}/g;
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$result =~ s/%IP%/$remote_ip/g;
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}
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else {
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# shouldn't get here?
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$result = "Blocked by $dnsbl";
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}
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}
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}
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else {
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$self->log(LOGERROR, "$dnsbl query failed: ", $res->errorstring)
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unless $res->errorstring eq "NXDOMAIN";
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}
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if ($result) {
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#kill any other pending I/O
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$conn->notes('dnsbl_sockets', undef);
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$result = join("\n", $self->qp->config('dnsbl_rejectmsg'), $result);
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return $conn->notes('dnsbl', $result);
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}
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}
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if ($sel->count) {
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# loop around if we have dns blacklists left to see results from
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return $self->process_sockets();
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}
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# er, the following code doesn't make much sense anymore...
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# if there was more to read; then forget it
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$conn->notes('dnsbl_sockets', undef);
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return $conn->notes('dnsbl', $result);
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}
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sub hook_rcpt {
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my ($self, $transaction, $rcpt, %param) = @_;
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# RBLSMTPD being non-empty means it contains the failure message to return
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if (defined $ENV{'RBLSMTPD'} && $ENV{'RBLSMTPD'} ne '') {
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my $result = $ENV{'RBLSMTPD'};
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my $remote_ip = $self->qp->connection->remote_ip;
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$result =~ s/%IP%/$remote_ip/g;
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my $msg = $self->qp->config('dnsbl_rejectmsg');
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$self->log(LOGINFO, "fail: $msg");
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return ($self->{_dnsbl}->{DENY}, join(' ', $msg, $result));
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}
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my $note = $self->process_sockets or return DECLINED;
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if ( $self->ip_whitelisted() ) {
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$self->log(LOGINFO, "skip: whitelisted");
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return DECLINED;
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};
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if ( $rcpt->user =~ /^(?:postmaster|abuse|mailer-daemon|root)$/i ) {
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$self->log(LOGWARN, "skip: don't blacklist special account: ".$rcpt->user);
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return DECLINED;
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}
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$self->log(LOGINFO, 'fail');
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return ($self->{_dnsbl}->{DENY}, $note);
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}
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sub hook_disconnect {
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my ($self, $transaction) = @_;
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$self->qp->connection->notes('dnsbl_sockets', undef);
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return DECLINED;
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}
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=head1 USAGE
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Add the following line to the config/plugins file:
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dnsbl [ reject_type disconnect ] [loglevel -1]
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=head2 reject_type
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To immediately drop the connection (since some blacklisted servers attempt
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multiple sends per session), set the optional argument I<reject_type> to
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"disconnect" on the config/plugin entry. In most cases, an
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IP address that is listed should not be given the opportunity to begin
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a new transaction, since even the most volatile blacklists will return
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the same answer for a short period of time (the minimum DNS cache period).
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=head2 loglevel
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Adjust the quantity of logging for this plugin. See docs/logging.pod
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=head1 CONFIG FILES
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=over 4
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This plugin uses the following configuration files. All are optional. Not
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specifying dnsbl_zones is like not using the plugin at all.
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=item dnsbl_zones
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Normal ip based dns blocking lists ("RBLs") which contain TXT records are
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specified simply as:
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relays.ordb.org
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spamsources.fabel.dk
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To configure RBL services which do not contain TXT records in the DNS,
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but only A records (e.g. the RBL+ at http://www.mail-abuse.org), specify your
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own error message to return in the SMTP conversation after a colon e.g.
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rbl-plus.mail-abuse.org:You are listed at - http://http://www.mail-abuse.org/cgi-bin/lookup?%IP%
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The string %IP% will be replaced with the IP address of incoming connection.
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Thus a fully specified file could be:
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sbl-xbl.spamhaus.org
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list.dsbl.org
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rbl-plus.mail-abuse.ja.net:Listed by rbl-plus.mail-abuse.ja.net - see <URL:http://www.mail-abuse.org/cgi-bin/lookup?%IP%>
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relays.ordb.org
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=item dnsbl_allow
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List of allowed ip addresses that bypass RBL checking. Format is one entry per line,
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with either a full IP address or a truncated IP address with a period at the end.
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For example:
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192.168.1.1
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172.16.33.
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NB the environment variable RBLSMTPD is considered before this file is
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referenced. See below.
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=item dnsbl_rejectmsg
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A textual message that is sent to the sender on an RBL failure. The TXT record
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from the RBL list is also sent, but this file can be used to indicate what
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action the sender should take.
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For example:
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If you think you have been blocked in error, then please forward
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this entire error message to your ISP so that they can fix their problems.
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The next line often contains a URL that can be visited for more information.
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=back
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=head1 Environment Variables
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=head2 RBLSMTPD
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The environment variable RBLSMTPD is supported and mimics the behaviour of
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Dan Bernstein's rblsmtpd. The exception to this is the '-' char at the
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start of RBLSMTPD which is used to force a hard error in Dan's rblsmtpd.
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NB I don't really see the benefit
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of using a soft error for a site in an RBL list. This just complicates
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things as it takes 7 days (or whatever default period) before a user
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gets an error email back. In the meantime they are complaining that their
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emails are being "lost" :(
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=over 4
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=item RBLSMTPD is set and non-empty
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The contents are used as the SMTP conversation error.
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Use this for forcibly blocking sites you don't like
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=item RBLSMTPD is set, but empty
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In this case no RBL checks are made.
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This can be used for local addresses.
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=item RBLSMTPD is not set
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All RBL checks will be made.
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This is the setting for remote sites that you want to check against RBL.
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=back
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=head1 Revisions
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See: http://cvs.perl.org/viewcvs/qpsmtpd/plugins/dnsbl
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=cut
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