How to Find SMTP Mail Server Name and Port

Question

Hi
There
How to Find SMTP Mail Server Name and Port Number 
if i have the ip of server in C# asp.net

thanks in advance

SALIL NAYAK

Answer 1

Hostname is easy .  Port not so much...  Without checking every Port for a valid SMTP response I think you are pretty much out of luck on that.

Answer 2

name means SMTP or MAIL  what are the basic port no have to be check

Answer 3

By using the class below you can get the mx record of a domain.

After that you can try port 25 first and then other ports.

    public class Mx
    {
        public Mx()
        {
        }
        [DllImport("dnsapi", EntryPoint = "DnsQuery_W", CharSet = CharSet.Unicode, SetLastError = true, ExactSpelling = true)]
        private static extern int DnsQuery([MarshalAs(UnmanagedType.VBByRefStr)]ref string pszName, QueryTypes wType, QueryOptions options, int aipServers, ref IntPtr ppQueryResults, int pReserved);

        [DllImport("dnsapi", CharSet = CharSet.Auto, SetLastError = true)]
        private static extern void DnsRecordListFree(IntPtr pRecordList, int FreeType);

        public static string[] GetMXRecords(string domain)
        {

            IntPtr ptr1 = IntPtr.Zero;
            IntPtr ptr2 = IntPtr.Zero;
            MXRecord recMx;
            if (Environment.OSVersion.Platform != PlatformID.Win32NT)
            {
                throw new NotSupportedException();
            }
            ArrayList list1 = new ArrayList();
            int num1 = Mx.DnsQuery(ref domain, QueryTypes.DNS_TYPE_MX, QueryOptions.DNS_QUERY_BYPASS_CACHE, 0, ref ptr1, 0);
            if (num1 != 0)
            {
                throw new Win32Exception(num1);
            }
            for (ptr2 = ptr1; !ptr2.Equals(IntPtr.Zero); ptr2 = recMx.pNext)
            {
                recMx = (MXRecord)Marshal.PtrToStructure(ptr2, typeof(MXRecord));
                if (recMx.wType == 15)
                {
                    string text1 = Marshal.PtrToStringAuto(recMx.pNameExchange);
                    list1.Add(text1);
                }
            }
            Mx.DnsRecordListFree(ptr2, 0);
            return (string[])list1.ToArray(typeof(string));
        }

        private enum QueryOptions
        {
            DNS_QUERY_ACCEPT_TRUNCATED_RESPONSE = 1,
            DNS_QUERY_BYPASS_CACHE = 8,
            DNS_QUERY_DONT_RESET_TTL_VALUES = 0x100000,
            DNS_QUERY_NO_HOSTS_FILE = 0x40,
            DNS_QUERY_NO_LOCAL_NAME = 0x20,
            DNS_QUERY_NO_NETBT = 0x80,
            DNS_QUERY_NO_RECURSION = 4,
            DNS_QUERY_NO_WIRE_QUERY = 0x10,
            DNS_QUERY_RESERVED = -16777216,
            DNS_QUERY_RETURN_MESSAGE = 0x200,
            DNS_QUERY_STANDARD = 0,
            DNS_QUERY_TREAT_AS_FQDN = 0x1000,
            DNS_QUERY_USE_TCP_ONLY = 2,
            DNS_QUERY_WIRE_ONLY = 0x100
        }

        private enum QueryTypes
        {
            DNS_TYPE_MX = 15
        }

        [StructLayout(LayoutKind.Sequential)]
        private struct MXRecord
        {
            public IntPtr pNext;
            public string pName;
            public short wType;
            public short wDataLength;
            public int flags;
            public int dwTtl;
            public int dwReserved;
            public IntPtr pNameExchange;
            public short wPreference;
            public short Pad;
        }
    }

Answer 4

You may also choose to implement a 3rd party port scanner which can be launched as a Process. After you use the 3rd party scanner you can analyze the subset of available ports by querying each with a helo command to verify SMTP existence.

Be forwarned that this activity is often viewed as hacking and may get you banned.  As far as legality, you should consult a lawyer.

Answer 5

howto get port no

Answer 6

Commonly used smtp port is 25.

As Brian mentioned using an smtp server unauthorized may cause you some legal problems.. Sending helo command is a good idea. You can use this method to send helo command and check the response.

foreach (string str in Mx.GetMXRecords(domainName))
            {
                TcpClient insTcpClient=null;
                    //MessageBox.Show(str);
                    insTcpClient = new TcpClient(str, 25);
                    NetworkStream ns = insTcpClient.GetStream();

                    byte[] recievedMessage = new byte[insTcpClient.ReceiveBufferSize];
                    ns.Read(recievedMessage, 0, insTcpClient.ReceiveBufferSize);
                    //MessageBox.Show(Encoding.ASCII.GetString(recievedMessage));

                    string messageToSend = "HELO\r\n";
                    byte[] buffer = System.Text.Encoding.GetEncoding(1254).GetBytes(messageToSend);
                    ns.Write(buffer, 0, buffer.Length);

                    recievedMessage = new byte[insTcpClient.ReceiveBufferSize];
                    ns.Read(recievedMessage, 0, insTcpClient.ReceiveBufferSize);
                    //MessageBox.Show(Encoding.ASCII.GetString(recievedMessage));

                   insTcpClient.GetStream().Close();
                    insTcpClient.Close();
                }

            }

Answer 7

As Brian mentioned using an smtp server unauthorized may cause you some legal problems.. Sending helo command is a good idea.

That is certainly true, but in this case I was referring to the fact that advanced firewalls watch for port scanning-like activity and will report such activity to the network administrator along with your IP address.

---

Good coding involves knowing one's logical limits and expanding them as necessary.

Answer 8

On top of that in today's world of SPAM, you are blocked from sending or relaying of an SMTP server unless your IP Address is authorized.  You might not even get a valid HELO response if you aren't authorized.  Also, as Brian said that an advanced security system would likely lock you once you started a port scan.  What are you trying to accomplish?  Not to be a cynic but if I wanted you relaying mail of my server I would give you this the host address and port, this sound like something a botnet would do to send out spam.