Walkthrough: Creating an HTML Email Template with Razor and Razor Class Libraries and Rendering it from a .NET Standard Class Library

tldr;

HtmlEmailExample

Full Code: https://github.com/scottsauber/RazorHtmlEmails

 

Usually I don’t blog walkthroughs and instead prefer to go a little deeper on a small topic, but I thought it would be useful to blog our approach on generating HTML emails using Razor for an ASP.NET Core insurance application at work.

 

If you’re looking to generate HTML Emails outside of ASP.NET Core (such as a Console app), I also recommend checking out Derek Comartin‘s post: Using Razor in a Console Application (outside of ASP.NET Core MVC).

 

Purpose

HTML emails are the absolute worst.  Inlined styles.  Nested tables.  Different apps and platforms render the markup differently.  It’s an absolute train wreck.  However, sending plain text emails isn’t a great way to impress your users and often makes emails look fake or like spam.  So fine, HTML emails.  Let’s do it.

 

What I would like to do is create an HTML Email Template library, and let developers focus on the content of their email, and not worry about the extra cruft that is HTML Emails.

 

Also, I want to be able to generate these HTML Emails from within a .NET Class Library (be it .NET Standard or .NET Core), so that the sending of the emails happens right next to all my other business logic.

 

So at a high level, the requirements are:

  1. Create a base Email Layout to enforce a consistent layout (Header, Footer, base styles, etc.) and to hide the complexity of HTML Email Layouts.
  2. Create re-usable HTML Email components (such as buttons) to enforce consistent styling and hide the complexity of the implementation of the HTML Email components.
  3. Use Razor.
  4. Be able to call it from a .NET Standard or .NET Core Class Library.

 

Razor checks the box for #1, because it already has the concept of a Layout view and a child view.  It also is a good fit for #2, because it lets you re-use UI components via Partials (among other methods).  In fact, you can actually achieve #1, #2, and #3 in regular ASP.NET 4.x fairly easily.  However, I haven’t ever been able to achieve #4 in regular ASP.NET or pre-2.1 ASP.NET Core.  That is, I want to use Razor in a non-ASP.NET/ASP.NET Core setting such as Class Libraries.

 

It’s super common for applications to put their business logic in a Class Library to remove any dependency on the UI project and to allow that logic to be re-used across other applications.  However, when I tried to send HTML Emails from a Class Library in ASP.NET 4.x and ASP.NET Core pre-2.1, I couldn’t figure out how to get the Class Library to find the Views I was creating and ultimately I gave up.

 

Enter Razor Class Libraries

I won’t go into much detail about Razor Class Libraries, when the documentation already does a fantastic job, but the basic idea behind them is that you can share UI between multiple ASP.NET Core applications.  This UI can be Views, Controllers, Razor Pages, etc.

 

The simplest way to think about Razor Class Libraries is if you add a View in your Razor Class Library, it essentially gets copied down into that same relative path into your main application.  So if you add an Index.cshtml file to the /Views/Home path of your Razor UI Class Library, then that file will be available at /Views/Home/Index.cshtml of your ASP.NET Core Application.  That’s pretty sweet and useful. But the question is would it find those files in a normal .NET Standard Class Library?  The answer is – yes.

 

One potential gotcha: Make sure that your Views have unique names/paths.  If you make an HTML Email view that matches the path of an actual like MVC View or Razor Page, then they will conflict.  Therefore, I try to make my folder and/or view names clearly unique like “ConfirmAccountEmail.cshtml” which is unlikely to have a matching route on my ASP.NET Core application.

 

Alright then, let the walkthrough begin!

 

Create an ASP.NET Core Web Application

First – create an ASP.NET Core Web Application or you can use an existing ASP.NET Core Web App.  It doesn’t really matter what it is.

With Visual Studio:

  1. File
  2. New Project
  3. ASP.NET Core Web Application
    1. I just called it RazorHtmlEmails.AspNetCore
  4. Web Application
  5. OK

 

Or with the command line:

  1. dotnet new sln -n RazorHtmlEmails
  2. dotnet new razor -n RazorHtmlEmails.AspNetCore
  3. dotnet sln RazorHtmlEmails.sln add RazorHtmlEmails.AspNetCore

GitHub commit here

 

Create a Razor Class Library

Next – create an ASP.NET Core Razor Class Library.

With Visual Studio:

  1. Right-click the Solution
  2. Add
  3. New Project
  4. ASP.NET Core Web Application
    1. I just called it RazorHtmlEmails.RazorClassLib
  5. Razor Class Library
  6. OK

 

Or… with the command line:

  1. dotnet new razorclasslib -n RazorHtmlEmails.RazorClassLib
  2. dotnet sln RazorHtmlEmails.sln add RazorHtmlEmails.RazorClassLib

 

After you’ve created your Razor Class Library, delete out the Areas folder, because we won’t need it.

GitHub commit here

 

Create the RazorViewToStringRenderer class

Tucked away in the aspnet/Entropy GitHub repo is the RazorViewToStringRenderer which shows you how to take a Razor View and render it to an HTML string.  This will be perfect for taking our Razor View, converting it to a string of HTML, and being able to stick the HTML into the body of an email.

 

Add this class to your Razor Class Library you just created.  I tucked mine under a folder called Services and then created an Interface for it called IRazorViewToStringRenderer:

GitHub commit here

 

Create your base HTML Email Layout

The next step in the process is we are going to leverage Razor’s Layout system to create a base HTML Email Layout.  There are many HTML Email Layout templates out there so you don’t have to write one yourself (and trust me… if you’ve never seen HTML Email code before, you’re not going to want to write this yourself).

I’m picking this one from Litmus, which is the leading vendor  (as far as I know) for testing your HTML Emails on multiple different platforms, devices, and applications.  No they didn’t pay me to say that (although if someone from Litmus is reading this, it’d be cool if you did).

The layout looks like this:

HtmlEmailExample

 

However, all I really care about for the layout is everything outside of the white box for my layout.  Inside the white box will change based on whatever I’m sending (Email Registration Confirmations, Forgot Password requests, Password Updated Alerts, etc.).

 

HtmlEmailLayout

Steps:

  1. In your Razor UI Class Library, create a /Views/Shared folder
  2. Add an EmailLayout.cshtml to that folder
  3. Add the following code and try not to pass out

 

When you finish throwing up in your mouth, let’s look at a couple important bits. Line 165 has the RenderBody() call which is where the white box is and where our child view will be placed dynamically based on the email I’m sending.

 

Another interesting spot is line 142 where I’m dynamically pulling an EmailTitle property from ViewDataViewData allows us to pass messages from a child view up to the parent view.  In the email screenshot above, this is the “Welcome” hero text.

 

ViewData

 

In a real application, I would have pulled that Welcome text down to the child view as well, but I left that as a demonstration of the ability for the child view to dynamically change the parent EmailLayout.  Some more examples of what you could do with ViewData could be the child view wants to dictate which Logo to use or what color the background is, or literally anything you want.  This is simply just leveraging a feature that’s been part of MVC for a long time.

 

 

Now that we’ve finished the Email Layout, let’s look at adding a custom button component.

GitHub commit here

 

Create a HTML Email Button Partial for re-usability

The next thing I want to do is start to make reusable components via partial views in order to abstract away the complexity of certain HTML Email components, as well as always providing a consistent look to the end user.

 

A good example of this is the button:

EmailButton

 

All that really needs to be dynamic about this is the text and the link. That should be easy enough.

Steps:

  1. Under /Views/Shared add a EmailButtonViewModel.cs class
  2. Add the following code:

 

3. Add an EmailButton.cshtml file
4. Add the following code:

 

Now we can re-use buttons in our child views by simply doing this:

 

That saves us from copying and pasting that crazy table code around every time we need a button for our Emails, which is useful.

GitHub commit here

Create your HTML Email Content

Now we’ve got all of our foundation pieces in place, let’s start building on top of them. The last thing we need to do in our Razor Class Library is add our custom email.

 

  1. Add a new folder under Views called Emails. This folder will house all of our custom HTML Emails.
  2. Add a _ViewStart.cshtml and add the following code so that every HTML Email has the EmailLayout.cshtml we created above as its parent layout

3. Add a ConfirmAccount folder under /Views/Emails.  This folder will house our ConfirmAccount email logic.

4. Add a ConfirmAccountEmailViewModel.cs file with the following code:

5. Add a ConfirmAccount.cshtml file with the following code:

 

Right now is where it all starts to come together, and you can see the power of being able to use Razor to build out our HTML emails.  On our day-to-day emails that we build out for the rest of our application, we no longer have to worry about gross table syntax or inline style craziness, we can just focus on the custom content that makes up that HTML Email.

GitHub commit here

 

Create a .NET Standard (or .NET Core) Class Library

But one of the coolest things about this, is the fact that we can call this code from regular .NET Standard (or .NET Core) Class Libraries, and have it all “just work.”  This means we can share our email templates across multiple applications to provide the same look and feel across all of them, and have all that logic live right next to the rest of our business logic.

 

So let’s create a .NET Standard Class Library.  If you want you can create a .NET Core Library and it’ll work as well.

With Visual Studio:

  1. Right-click the Solution
  2. Add
  3. New Project
  4. Class Library (.NET Standard)
    1. I just called it RazorHtmlEmails.Common
  5. OK

 

Or with the command line:

  1. dotnet new classlib -n RazorHtmlEmails.Common -f netstandard2.0
  2. dotnet sln RazorHtmlEmails.sln add RazorHtmlEmails.Common

 

Then delete out Class1.cs

GitHub commit here

 

Call the RazorViewToStringRenderer in your business logic

Now it’s time to hook up the .NET Core Class Library to the Razor Class Library.

  1. In the .NET Core Class Library (.Common), add a reference to the Razor Class Library (.RazorEmailLib)
  2. Install MailKit, a fantastic cross-platform, .NET Core-friendly email library
  3. Create a class called RegisterAccountService that will house our business logic for creating the account and sending the email.

The interesting bits are lines 25, where we create our ConfirmAccountEmailViewModel with the link we want to use and line 27 where we pass that model into our RazorViewToStringRenderer, and get back our Email’s HTML body.

 

As an aside, for testing local emails without an email server, I love using Papercut.  It’s a simple install and then you’re up and going with an email server that runs locally and also provides an email client.  No Papercut didn’t pay me to say that either.  It’s free.  If some paid service that does the same thing as Papercut does and wants to sponsor this blog, feel free to reach out to me and get rejected because you will never get me to give up Papercut.

GitHub commit here

 

Hook it up to the UI

The last step we have to do is to hook this up to the UI.  I’m just going to hook this up on a GET request of the /Index page just for demo purposes.  In reality, you’d have an input form that takes registration and have this happen on the POST.

 

  1. In your .AspNetCore project, add a project reference to .Common
  2. In Startup.cs under ConfigureServices wire up the IRegisterAccountService and the IRazorViewToStringRendererto their implementations.

3. In /Pages/Index.cshtml.cs, call the IRegisterAccountService in the OnGetAsync method

GitHub commit here

 

And you’re done!  When I run the app, and open up Papercut, I get my email in all its glory.

RazorEmail

 

Going forward, anytime I need an email, I can simply leverage the EmailLayout and EmailButton infrastructure I’ve created to make creating HTML emails incredibly easy and less table-y which is a huge win.

 

Just a reminder if somehow you’ve made it this far, all the code is out here on GitHub.

 

Hope this helps!

46 thoughts on “Walkthrough: Creating an HTML Email Template with Razor and Razor Class Libraries and Rendering it from a .NET Standard Class Library

  1. it doesnt work when i am trying to call it from Web API. the problem cannot find view in GetView or FindView method always back with null

    Like

  2. Hi Scott,
    Great solution, however I hit one issue,
    If I call _razorViewToStringRenderer.RenderViewToStringAsync a few times in a row will be fine.
    But if I call
    _razorViewToStringRenderer.RenderViewToStringAsync and in the middle I call others services, when I call
    _razorViewToStringRenderer.RenderViewToStringAsync again the httpContext.RequestServices always zero, exception caught is the serviceprovider is disposed.
    Have you found similar issues to this?

    Many thanks
    Jim

    private ActionContext GetActionContext()
    {
    var httpContext = new DefaultHttpContext();
    httpContext.RequestServices = _serviceProvider;
    return new ActionContext(httpContext, new RouteData(), new ActionDescriptor());
    }

    Like

    • Hey Jim,

      I have not hit this issue. What I would look for is to see if one of your services is using the IServiceProvider directly and manipulating it in some way. It being disposed is a little odd. Any chance you could share code of what’s going on so I could take a deeper look?

      Like

      • Hi Scott, many thanks for your quick reply, no the other service does not use IServiceProvider directly. And one thing if the service use UserManager and the the ServiceProvider injected into the RazorViewToStringRendered constructor will be null. I will get the source code soon to share. Thanks again.

        Liked by 1 person

      • This will work:
        var infoEmail = _configuration.GetSection(“Email:InfoEmail”).Value;
        var body = await _emailTemplateService.RenderViewToStringAsync(“/Views/Template/ConfirmAccountEmail.cshtml”, model);
        var body2 = await _emailTemplateService.RenderViewToStringAsync(“/Views/Template/ConfirmAccountEmail.cshtml”, model);

        await _postmarkEmailService.SendAsync(notification.Email, “Confirm your registration”, body);
        await _postmarkEmailService.SendAsync(infoEmail, “New member registration”, body2);

        This will NOT work:
        var infoEmail = _configuration.GetSection(“Email:InfoEmail”).Value;
        var body = await _emailTemplateService.RenderViewToStringAsync(“/Views/Template/ConfirmAccountEmail.cshtml”, model);
        await _postmarkEmailService.SendAsync(notification.Email, “Confirm your registration”, body);

        var body2 = await _emailTemplateService.RenderViewToStringAsync(“/Views/Template/ConfirmAccountEmail.cshtml”, model);
        await _postmarkEmailService.SendAsync(infoEmail, “New member registration”, body2);

        this is the postmarkService only use Iconfiguration, and not only postmarkService, most of the services, the problem is with hpptcontext.RequestServices which assigned by serviceprovider.

        public class PostmarkEmailService : IPostmarkEmailService
        {
        protected readonly IConfiguration _config;
        private readonly PostmarkClient _client;
        private readonly ILogger _logger;
        private readonly bool _emailEnabled;
        private readonly string _from;
        private readonly string _bcc;
        private readonly string _emailOverride;

        public PostmarkEmailService(IConfiguration config
        //ILoggerFactory loggerFactory
        )
        {
        //_logger = loggerFactory.CreateLogger();
        _config = config;
        _client = new PostmarkClient(_config.GetSection(“Email:PostmarkApiKey”).Value);
        _emailEnabled = _config.GetSection(“Email:Enabled”).Value.ToLower() == “true”;
        _from = _config.GetSection(“Email:From”).Value;
        _bcc = null == _config.GetSection(“Email:Bcc”) ? string.Empty : _config.GetSection(“Email:Bcc”).Value;
        _emailOverride = null == _config.GetSection(“Email:Override”) ? string.Empty : _config.GetSection(“Email:Override”).Value;

        }

        Many thanks
        Jimy

        Like

  3. So this essentially still requires an ASP project? How do you test it? How do you get the dependencies it needs in a test project?

    Like

  4. Scott, you rock. I just implemented this in an Asp.Net Core Web API that sends email notifications, and it’s so much better than what I was doing before.

    Liked by 1 person

  5. Just want to say this walk-through was extremely helpful in implementing email sending in my app!

    One tip I would like to pass on: Do your styles properly with styles defined in the header like it was a standard web-page – then run it through an inliner such as PreMailer (free – on Nuget) and it will magically move all those styles in line.

    I updated RazorViewToStringRenderer to include such a call and it works great!

    Like

  6. This is absolutely awesome, I got this up and running in no time. I included PreMailer.Net to inline my css styles in my RazorViewToStringRenderer so I can design my templates using classes, it worked very well for me!

    Liked by 1 person

  7. Hi great write up and works striaght out of the box as it is.
    However I’ve been trying to implement this into a WebAPI application. Application structure is MVC talking to a WebAPI backend. However when I call the _viewEngine.GetView this never finds my view? any help would be great

    Like

  8. Hi! Thank you so much for this.
    I have an old Asp.Net MVC application which I want to add beautiful email templates too but since your walk through is for .net core is there a way for me to adapt it to my project.
    Thanks in anticipation.

    Like

  9. Hi Scott!
    Great post!
    The only thing I want to ask, are there any possible performance issues, having 500+ of email?
    Should I think on replacing services.AddScoped to singleton, or caching the template somehow?
    What will be the most expensive operation in your solution and how to speed it up?
    Thanks a lot!

    Like

    • Hey Danyl – you should be able to make it a Singleton in theory, but I haven’t tried it. As far as performance, I would assume making it a Singleton is pretty negligible, to construct this since there’s not much going on, but I would benchmark it if that matters to your scenario.

      I would assume the slowest part will be generating the HTML from the Razor template, but not much you can really do there since that logic happens inside the RazorViewEngine from ASP.NET Core. This is definitely one of those things where you are trading off less performance for improved developer productivity and long-term maintenance. So if your situation requires performance, then you may have to re-evaluate that trade off and just deal with housing the HTML logic in strings or something rather in Razor.

      I would just try the 500 emails at once though and set a baseline and see if that baseline is good enough for your scenario.

      Like

  10. I’m a newbie trying to follow your steps and it seems that some of your steps are missing, like maybe a screenshot is not rendering. You say:

    Add the following code:

    3. Add an EmailButton.cshtml file
    4. Add the following code:

    Now we can re-use buttons in our child views by simply doing this:

    Like

      • Randy – no problem! Was just circling back to this and glad to see all is well. Curious if there’s anything I can do to make them not show up as false positives for ads… if you have any ideas let me know! Thanks.

        Like

  11. I’m trying to render a razor view from a aspnetcore 2.2 BackgroundService. Essentially I have a service sleeping in the background that wakes up and sends out emails of various types: Appointment Reminders, Reports to stake holders etc, etc.

    Your code works great until I try to render a view that has TagHelpers in it. When the engine tries to resolve the tag helpers it throws an ArgumentOutOfRange exception.

    I think the problem is that the HttpContext that is created in your code has no routing information in it, and the TagHelper requires that routing info to translate ‘asp-controller’ and ‘asp-action’ into html.

    I have seen other people use IHttpContextAccessor to get a legit context, but naturally the returned context is always null in the context of a Background Service (Makes sense to me, unless I’m missing something!?).

    Any thoughts on how to solve this? I hate to hardcode links in every view that I could potentially want to render to a string.

    Here is the stacktrace:
    at System.ThrowHelper.ThrowArgumentOutOfRange_IndexException()
    at System.Collections.Generic.List`1.get_Item(Int32 index)
    at Microsoft.AspNetCore.Mvc.Routing.UrlHelper.get_Router()
    at Microsoft.AspNetCore.Mvc.Routing.UrlHelper.GetVirtualPathData(String routeName, RouteValueDictionary values)
    at Microsoft.AspNetCore.Mvc.Routing.UrlHelper.Action(UrlActionContext actionContext)
    at Microsoft.AspNetCore.Mvc.UrlHelperExtensions.Action(IUrlHelper helper, String action, String controller, Object values, String protocol, String host, String fragment)
    at Microsoft.AspNetCore.Mvc.ViewFeatures.DefaultHtmlGenerator.GenerateActionLink(ViewContext viewContext, String linkText, String actionName, String controllerName, String protocol, String hostname, String fragment, Object routeValues, Object htmlAttributes)
    at Microsoft.AspNetCore.Mvc.TagHelpers.AnchorTagHelper.Process(TagHelperContext context, TagHelperOutput output)
    at Microsoft.AspNetCore.Razor.TagHelpers.TagHelper.ProcessAsync(TagHelperContext context, TagHelperOutput output)
    at Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperRunner.d__0.MoveNext()
    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
    at AspNetCore.Views_Shared__email_Layout2.<b__35_1>d.MoveNext() in C:\Workspace\GroomShop\GroomShop.Web\Views\Shared\_email_Layout2.cshtml:line 144

    Like

  12. To avoid the exception being generated in the above message, I have modified GetActionContext() to have a Router in its collection as seen below. This solves the exception problem but unfortunately now the tag-helpers incorrectly resolve to href=””. Hopefully someone has seen this before and has a recommendation / solution?

    private ActionContext GetActionContext()
    {
    var httpContext = new DefaultHttpContext
    {
    RequestServices = this._serviceProvider,
    };

    var attrRouter = this._serviceProvider.GetRequiredService();

    var rd = new RouteData();
    //rd.Values.Add(“controller”, “Email”);
    //rd.Values.Add(“action”, “AppointmentReminder”);
    rd.Routers.Add(attrRouter);

    var result = new ActionContext(httpContext, rd, new ActionDescriptor());

    return result;
    }

    Like

  13. i am getting an invalid operation exception : InvalidOperationException: The model item passed into the ViewDataDictionary is of type ‘HTMLEmails.Views.Emails.ConfirmAccount.ConfirmAccountEmailViewModel’, but this ViewDataDictionary instance requires a model item of type ‘NetCoreApp.Models.LoginViewModel’. although i did every thing exactly the same.
    using asp.net core 2.2

    Like

    • Problem solved!
      there was a conflict between the view start of the original project and the view start of the HTML emails project, moving the latter view start to the emails folder solved the problem.

      Thanks for the great post!

      Like

    • Hi Bipin – it’s on my list to upgrade all these examples to 3.0. Nothing off hand jumps out at me as being problematic in 3.0, but I admittedly haven’t tried it yet. I will probably get to this next week. Thanks!

      Like

      • Hi , Thanks
        I tried to update but I was not able to make this work on .NET core 3.
        I think , there are some namespaces that has changed in .NET core 3.

        My current trick.
        so the current sample requires .NET Core 2.2 SDK to build but it runs fines on .NET core 3.

        Like

  14. THANK YOU!!!
    I’ve always thought that it had to be “easy” to get Razor views to work with server side rendering to a string, but I have had one heck of a time finding a way to do this. In my opinion this needs to be written up on MSDN as the “official” way to do templating in .NET Core. I’m not using this for emails but for HTML report to PDF generation. It’s rather easy to take a HTML document and go to PDF but the missing link I had was being able to make the HTML on the server side and handing it off to the PDF renderer. This solves that problem in such an elegant way!

    Like

    • Hey Mike – I really appreciate the comment. That’s a great point about HTML => PDF and is a great use case for this type fo thing as well. Thanks again for taking the time to leave the comment, I really appreciate it.

      Like

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