diff --git a/DnsServerCore.ApplicationCommon/IDnsPostProcessor.cs b/DnsServerCore.ApplicationCommon/IDnsPostProcessor.cs
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+++ b/DnsServerCore.ApplicationCommon/IDnsPostProcessor.cs
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+/*
+Technitium DNS Server
+Copyright (C) 2022  Shreyas Zare (shreyas@technitium.com)
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+
+using System.Net;
+using System.Threading.Tasks;
+using TechnitiumLibrary.Net.Dns;
+
+namespace DnsServerCore.ApplicationCommon
+{
+    /// <summary>
+    /// Lets a DNS App process a response generated by the DNS server allowing it to make changes to the final response that will be sent to the client.
+    /// </summary>
+    public interface IDnsPostProcessor
+    {
+        /// <summary>
+        /// Allows a DNS App to process the response generated by the DNS server for a given request. This method is called by the DNS Server after a response is generated before being sent to the client. Response returned by this method will be the final response that gets sent to the client.
+        /// </summary>
+        /// <param name="request">The incoming DNS request received by the DNS server.</param>
+        /// <param name="remoteEP">The end point (IP address and port) of the client making the request.</param>
+        /// <param name="protocol">The protocol using which the request was received.</param>
+        /// <param name="response">The DNS response that was generated by the DNS server for the received DNS request.</param>
+        /// <returns>The final DNS response that the DNS server will send to the client.</returns>
+        Task<DnsDatagram> PostProcessAsync(DnsDatagram request, IPEndPoint remoteEP, DnsTransportProtocol protocol, DnsDatagram response);
+    }
+}