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Använd DNS Blocklist för att förhindra spam
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Kategori: Internet
Inlagt: 2004-10-01
Läst: 1313
Inlagt av: Staffan Berg
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Beskrivning |
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Ett exempel för att upptäcka och förhindra spam. Det fungerar i korthet så att du verifierar emot en DNS Blocklist-källa (t ex www.spamhaus.org). Om du exempelvis vill kontrollera IP-adressen 60.70.80.90 skapar du först en DNS-fråga till sbl.spamhaus.org med samma IP-adress inskriven baklänges enligt: query dns: 90.80.70.60.sbl.spamhaus.org. Får du då tillbaka bokstaven A så är det ett spam annars inte.
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Kod |
unit spamchck;
interface
//Query's the spamhaus.org database of spammers
uses Classes, SysUtils, {$IFDEF SYNAPSE}SynaUtil, SynSock{$ELSE}WinSock{$ENDIF};
type
TSpamCheck = class (TObject)
protected
public
FDNSBL:String; //DNS BlockList
constructor Create;
function IsSpammer (IP:String):Integer; overload;
function IsSpammer (MailHeader:TStrings):Integer; overload;
end;
implementation
{ TSpamCheck }
constructor TSpamCheck.Create;
begin
inherited;
FDNSBL := 'sbl-xbl.spamhaus.org';
// alternatively use sbl.spamhaus.org (spam) or
// xbl.spamhaus.org (open relays, proxys)
// or an alternative source DNSBL source.
// the sbl-xbl is the combined list.
end;
function TSpamCheck.IsSpammer(IP: String): Integer;
var RevIP:String;
i:Integer;
p:PHostEnt;
begin
//Query the database
//First, reverse the IP
Result := -1;
{$IFDEF SYNAPSE}
if IsIP (IP) then
{$ENDIF}
begin
//Reverse the IP
RevIP := '';
for i:=0 to 2 do
begin
RevIP := '.'+Copy (IP, 1, pos ('.', IP)-1) + RevIP;
IP := Copy (IP, pos('.', IP)+1, maxint);
end;
RevIP := IP + RevIP;
//Now, query the database:
RevIP := RevIP + '.' + FDNSBL;
p := GetHostByName (PChar(RevIP));
if Assigned (p) then
begin //Results come back as 127.0.0.x where x > 1
// 127.0.0.2 = spam
// 127.0.0.4 = open relay etc.
Result := byte(p^.h_addr^.S_un_b.s_b4);
end
else //no dns entry found, mark it as safe:
Result := 0;
end;
end;
function TSpamCheck.IsSpammer(MailHeader: TStrings): Integer;
var v,ip:String;
i,r:Integer;
begin
//Parse a email header
//Look for 'Received' header
//extract IP address, assuming form 'Received: from (a.b.c.d) by (w.x.y.z)
//Validate this IP address at spamhaus.
i := 0;
Result := -1;
while i
begin
if pos ('received: ', lowercase (MailHeader[i])) = 1 then
begin
v := MailHeader[i];
//search for additional headers:
while ((i+1)
(MailHeader[i+1]<>'') and
(MailHeader[i+1][1]=' ') do
begin
inc (i);
v := v+MailHeader[i];
end;
//v now contains one line, find from ip address:
v := lowercase (v);
//searching for:
//Received: from somehost.com (1.2.3.4).
v := copy (v, pos ('from', v)+4, maxint);
v := copy (v, pos ('(', v)+1, maxint);
v := copy (v, 1, pos (')', v)-1);
if pos ('[', v)>0 then
//valid format is also:
//Received: from somehost.com (somehost.com [1.2.3.4])
begin
v := copy (v, pos ('[', v)+1, maxint);
v := copy (v, 1, pos (']', v)-1);
end;
Result := IsSpammer (v);
//a single received line is sufficient
if Result > 0 then
break;
//
end;
inc (i);
end;
end;
end.
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