dotnet-core_mail-server/MailServer/GetDNSEntries.cs

using DnsClient;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

namespace SMTPServer
{
    public class GetDNSEntries
    {
        public static async System.Threading.Tasks.Task<string[]> GetMXRecordAsync(string domain) => await GetMXRecordAsync(domain, 0);

        public static async System.Threading.Tasks.Task<string[]> GetMXRecordAsync(string domain, int nr)
        {
            var lookup = new LookupClient();
            var result = await lookup.QueryAsync(domain, QueryType.MX);

            var records =  result.AllRecords.ToArray();

            //ToDo priority sorting

            var rec = new string[records.Length];

            for(int i = 0; i < records.Length; i++)
            {
                var str = records[i].RecordToString();
                var s = str.Split(' ');
                if (s.Length == 1)
                {
                    rec[i] = s[0];
                } else if (s.Length == 2)
                {
                    rec[i] = s[1];
                } else
                {
                    rec[i] = null;
                }
            }

            return rec;
            /*
            foreach (var r in result.AllRecords)
            {
                Console.WriteLine(r.RecordToString());
            }*/
        }

        public static async System.Threading.Tasks.Task<string[]> GetIPAddressFromDnsArrayAsync(string[] dnsnames)
        {
            var ips = new string[dnsnames.Length];
            for(int i = 0; i < dnsnames.Length; i++)
            {
                ips[i] = await GetIpFromDnsNameAsync(dnsnames[i]);
            }

            return ips;
        }

        public static async System.Threading.Tasks.Task<string> GetIpFromDnsNameAsync(string dnsname)
        {
            var lookup = new LookupClient();
            var result = await lookup.QueryAsync(dnsname, QueryType.A);

            var records = result.AllRecords.ToArray();

            if (records.Length < 1) return null;
            return records[0].RecordToString();
        }
    }
}