Get SPF records from a Domain

Question

What are the ways to Check SPF records on a domain?

There is a website where i can do it manually using - http://www.mxtoolbox.com/SuperTool.aspx

How can i do it

Answer 1

Building on the answer by Martin Liversage, I've added some comments that explain what's going on, and adjusted to return multiple records if they exist.

My example also concatenates multiple strings in a TXT record rather than separating by line breaks.

I don't know if the if (dnsRecord.wType == DNS_TYPE_TEXT) line is really necessary considering that constraint is in the arguments to the DnsQuery function, but I preserved it from Martin's answer anyway.

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Runtime.InteropServices;
using System.Text;

namespace Util
{
    /// 

    /// Based on https://stackoverflow.com/a/11884174 (Martin Liversage)
    /// 
    class DnsInterop
    {
        private const short DNS_TYPE_TEXT = 0x0010;
        private const int DNS_QUERY_STANDARD = 0x00000000;
        private const int DNS_ERROR_RCODE_NAME_ERROR = 9003;
        private const int DNS_INFO_NO_RECORDS = 9501;


        public static IEnumerable GetTxtRecords(string domain)
        {
            var results = new List();
            var queryResultsSet = IntPtr.Zero;
            DnsRecordTxt dnsRecord;

            try
            {
                // get all text records
                // pointer to results is returned in queryResultsSet
                var dnsStatus = DnsQuery(
                  domain,
                  DNS_TYPE_TEXT,
                  DNS_QUERY_STANDARD,
                  IntPtr.Zero,
                  ref queryResultsSet,
                  IntPtr.Zero
                );

                // return null if no records or DNS lookup failed
                if (dnsStatus == DNS_ERROR_RCODE_NAME_ERROR
                    || dnsStatus == DNS_INFO_NO_RECORDS)
                {
                    return null;
                }

                // throw an exception if other non success code
                if (dnsStatus != 0)
                    throw new Win32Exception(dnsStatus);

                // step through each result
                for (
                    var pointer = queryResultsSet; 
                    pointer != IntPtr.Zero; 
                    pointer = dnsRecord.pNext)
                {
                    dnsRecord = (DnsRecordTxt)
                        Marshal.PtrToStructure(pointer, typeof(DnsRecordTxt));

                    if (dnsRecord.wType == DNS_TYPE_TEXT)
                    {
                        var builder = new StringBuilder();

                        // pointer to array of pointers
                        // to each string that makes up the record
                        var stringArrayPointer = pointer + Marshal.OffsetOf(
                            typeof(DnsRecordTxt), "pStringArray").ToInt32();

                        // concatenate multiple strings in the case of long records
                        for (var i = 0; i < dnsRecord.dwStringCount; ++i)
                        {
                            var stringPointer = (IntPtr)Marshal.PtrToStructure(
                                stringArrayPointer, typeof(IntPtr));

                            builder.Append(Marshal.PtrToStringUni(stringPointer));
                            stringArrayPointer += IntPtr.Size;
                        }

                        results.Add(builder.ToString());
                    }
                }
            }
            finally
            {
                if (queryResultsSet != IntPtr.Zero)
                {
                    DnsRecordListFree(queryResultsSet, 
                        (int)DNS_FREE_TYPE.DnsFreeRecordList);
                }
            }

            return results;
        }


        [DllImport("Dnsapi.dll", EntryPoint = "DnsQuery_W", 
            ExactSpelling = true, CharSet = CharSet.Unicode, 
            SetLastError = true)]
        static extern int DnsQuery(string lpstrName, short wType, int options, 
            IntPtr pExtra, ref IntPtr ppQueryResultsSet, IntPtr pReserved);


        [DllImport("Dnsapi.dll")]
        static extern void DnsRecordListFree(IntPtr pRecordList, int freeType);


        [StructLayout(LayoutKind.Sequential, CharSet = CharSet.Unicode)]
        struct DnsRecordTxt
        {
            public IntPtr pNext;
            public string pName;
            public short wType;
            public short wDataLength;
            public int flags;
            public int dwTtl;
            public int dwReserved;
            public int dwStringCount;
            public string pStringArray;
        }


        enum DNS_FREE_TYPE
        {
            DnsFreeFlat = 0,
            DnsFreeRecordList = 1,
            DnsFreeParsedMessageFields = 2
        }
    }
}