Program.cs

using DontPanic.TumblrSharp;
using DontPanic.TumblrSharp.Client;
using System;

namespace TumblrBotTest
{
    class Program
    {
        static void Main(string[] args)
        {

            // Tumblr.Client.CreatePostAsync(
            //     Tumblr.BlogName, PostData.CreateText("this is a text #cool #bot #wow")
            //     );

            // var me = Tumblr.Client.GetBlogInfoAsync(Tumblr.BlogName).Result;
            // Console.WriteLine(me.PostsCount);

            var inbox = Tumblr.Client.GetSubmissionPostsAsync(Tumblr.BlogName).Result;

            foreach (var message in inbox)
            {
                var msg = (AnswerPost)message;

                Console.WriteLine();

                Tumblr.Client.EditPostAsync(
                    Tumblr.BlogName, msg.Id, PostData.CreateAnswer(
                        "hello", null, PostCreationState.Published));
            }
            Console.ReadLine();
        }
    }
}

Tumblr.cs

using DontPanic.TumblrSharp;
using DontPanic.TumblrSharp.Client;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace TumblrBotTest
{
    public static class Tumblr
    {
        const string CONSUMER_KEY;
        const string CONSUMER_SECRET;
        const string OAUTH_TOKEN;
        const string OAUTH_TOKEN_SECRET;
        
        static public TumblrClient Client;
        static public string BlogName { get; set; } = "somethinginterestingbot";

        static Tumblr()
        {
            Client = new TumblrClientFactory().Create<TumblrClient>(
                CONSUMER_KEY,
                CONSUMER_SECRET,
                new DontPanic.TumblrSharp.OAuth.Token(
                    OAUTH_TOKEN, OAUTH_TOKEN_SECRET));
        }
    }
}