for ASP.NET CORE 2.0 Email Render

ViewRenderService.cs

using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Abstractions;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.Razor;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.ViewFeatures;
using Microsoft.AspNetCore.Routing;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Threading.Tasks;

namespace Services
{
	public interface IViewRenderService
	{
		Task<string> RenderToStringAsync(string viewName);
		Task<string> RenderToStringAsync<TModel>(string viewName, TModel model);
		string RenderToString<TModel>(string viewPath, TModel model);
		string RenderToString(string viewPath);
	}

	public class ViewRenderService : IViewRenderService
	{
		private readonly IRazorViewEngine _viewEngine;
		private readonly ITempDataProvider _tempDataProvider;
		private readonly IServiceProvider _serviceProvider;
		private readonly IHttpContextAccessor _httpContextAccessor;

		public ViewRenderService(IRazorViewEngine viewEngine, IHttpContextAccessor httpContextAccessor,
			ITempDataProvider tempDataProvider,
			IServiceProvider serviceProvider)
		{
			_viewEngine = viewEngine;
			_httpContextAccessor = httpContextAccessor;
			_tempDataProvider = tempDataProvider;
			_serviceProvider = serviceProvider;
		}

		public string RenderToString<TModel>(string viewPath, TModel model)
		{
			try
			{
				var viewEngineResult = _viewEngine.GetView("~/", viewPath, false);

				if (!viewEngineResult.Success)
				{
					throw new InvalidOperationException($"Couldn't find view {viewPath}");
				}

				var view = viewEngineResult.View;

				using (var sw = new StringWriter())
				{
					var viewContext = new ViewContext()
					{
						HttpContext = _httpContextAccessor.HttpContext ?? new DefaultHttpContext { RequestServices = _serviceProvider },
						ViewData = new ViewDataDictionary<TModel>(new EmptyModelMetadataProvider(), new ModelStateDictionary()) { Model = model },
						Writer = sw
					};
					view.RenderAsync(viewContext).GetAwaiter().GetResult();
					return sw.ToString();
				}
			}
			catch (Exception ex)
			{
				throw new Exception("Error ending email.", ex);
			}
		}

		public async Task<string> RenderToStringAsync<TModel>(string viewName, TModel model)
		{
			var httpContext = _httpContextAccessor.HttpContext ?? new DefaultHttpContext { RequestServices = _serviceProvider };
			var actionContext = new ActionContext(httpContext, new RouteData(), new ActionDescriptor());

			using (var sw = new StringWriter())
			{
				var viewResult = _viewEngine.FindView(actionContext, viewName, false);

				// Fallback - the above seems to consistently return null when using the EmbeddedFileProvider
				if (viewResult.View == null)
				{
					viewResult = _viewEngine.GetView("~/", viewName, false);
				}

				if (viewResult.View == null)
				{
					throw new ArgumentNullException($"{viewName} does not match any available view");
				}

				var viewDictionary = new ViewDataDictionary(new EmptyModelMetadataProvider(), new ModelStateDictionary())
				{
					Model = model
				};

				var viewContext = new ViewContext(
					actionContext,
					viewResult.View,
					viewDictionary,
					new TempDataDictionary(actionContext.HttpContext, _tempDataProvider),
					sw,
					new HtmlHelperOptions()
				);

				await viewResult.View.RenderAsync(viewContext);
				return sw.ToString();
			}
		}

		public string RenderToString(string viewPath)
		{
			return RenderToString(viewPath, string.Empty);
		}

		public Task<string> RenderToStringAsync(string viewName)
		{
			return RenderToStringAsync<string>(viewName, string.Empty);
		}
	}
}

example:

var htmlBody = await _viewService.RenderToStringAsync("~/Views/Email/Policy.cshtml", model);