function TForm1.GetMxList(dns, dmn: string): TStringList;
var
  k: Integer;
  IdDNS:TIdDnsResolver;
begin
  Result := TStringList.Create;
  IdDNS := TIdDnsResolver.Create(nil);
  if dns = '' then dns := '192.168.1.1';
  IdDNS.Host := dns;
  IdDns.QueryRecords := [qtMX];
  try
    IdDns.Resolve(dmn);
    for k := 0 to IdDns.QueryResult.Count-1 do
      if IdDns.QueryResult[k] is TMxRecord then
        Result.Add(TMXRecord(IdDns.QueryResult[k]).ExchangeServer);
  finally
    IdDns.Free;
  end;
end;