In this article I will explain with an example, how to send Email using HTML Templates in ASP.Net Core.
Note: For more details on how to send email in ASP.Net Core, please refer my article Send Email in ASP.Net MVC Core.
 
 

Mail Server Settings in AppSettings.json file

The Mail Server settings are saved in the SMTP section as shown below.
Note: It is necessary to use the sender’s email address credentials while defining the Gmail SMTP Server Credentials as the sender’s email address must be same as the Gmail Username specified in credentials.
 
{
 "Smtp": {
    "Server": "smtp.gmail.com",
    "Port": 587,
    "EnableSsl": true,
    "FromAddress": "sender@gmail.com",
    "UserName": "sender@gmail.com",
    "Password": "GMAILor2STEP-PASSWORD",
    "DefaultCredentials": true
 }
}
 
 

Adding Email Template

The very first step is to Right Click the Project in the Solution Explorer and click Add and then New Item and then select HTML Page and name it as EmailTemplate.htm.
ASP.Net Core: Send Email using HTML Templates
 
 

Location of the EmailTemplate

The Email Template is placed inside the Template Folder (Directory) in Project Folder.
ASP.Net Core: Send Email using HTML Templates
 
 

Building HTML Template for Email Body

The HTML Template of the Email will be built by generating an HTML containing some placeholders which will be replaced with the actual content.
Advantage of creating templates instead of building HTML using String Builder class or String concatenation in code is that one can easily change the HTML of the template without changing the code.
The following HTML Email Template consists of four placeholders:
{UserName} – Name of the recipient.
{Url} – Url of the article.
{Title} – Title of the article.
{Description} – Description of the Article.
These placeholders will be replaced with the actual (real) values, when the email is being sent.
<html>
<head>
    <meta charset="utf-8"/>
    <title></title>
</head>
<body>
    <img style="background:black;" src="https://www.aspsnippets.com/assets/img/logo_ns.png"/><br /><br />
    <div style="border-top: 3px solid #61028D">&nbsp;</div>
    <span style="font-family: Arial; font-size: 10pt">
        Hello <b>{UserName}</b>,<br /><br />
        A new article has been published on ASPSnippets.<br /><br />
        <a style="color: #61028D" href="{Url}">{Title}</a><br />
        {Description}
        <br /><br />
        Thanks<br />
        ASPSnippets
    </span>
</body>
</html>
 
 

Namespaces

You will need to import the following namespaces.
using System.Net;
using System.Net.Mail;
 
 

Controller

The Controller consists of the following Action methods.

Action method for handling GET operation

Inside this Action method, simply the View is returned.
 

Action method for handling POST operation

Inside this Action method, first the necessary values are set which will be replaced with the placeholder inside the EmailTemplate file.

Setting Body of Email

For Body, the PopulateBody method is called and the path of the EmailTemplate file is read using IHostingEnvironment interface and its contents are read using the StreamReader class.
Note: For more details about IHostingEnvironment interface, please refer my article Using IHostingEnvironment in ASP.Net Core.
 
The placeholders are replaced with their respective values and the content of the HTML Email Template are returned.
Next, the formatted HTML body, email address (recepientEmail) and Subject are set into the respective properties of the object of MailMessage class.

Sending Email

Then, object of the SmtpClient class is created and the settings of the Mail Server such as Host, Port, EnableSsl, Username, Password, Sender email address (from) and DefaultCredentials are fetched from the SMTP section of the AppSettings.json file and are set into the respective properties of the SmtpClient class object.
And, the email is being sent using Send method of the SmtpClient class and success message is set into a ViewBag object.
public class HomeController : Controller
{
    private IWebHostEnvironment Environment { get; set; }
    private IConfiguration Configuration { get; set; }
 
    public HomeController(IConfiguration _configuration, IWebHostEnvironment environment)
    {
        this.Configuration = _configuration;
        this.Environment = environment;
    }
 
    publicIActionResult Index()
    {
        return View();
    }
 
    [HttpPost]
    public IActionResult SendEmail()
    {
        string name = "John";
        string title = "ASP.Net MVC Core Hello World Tutorial with Sample Program example";
        string url = "https://www.aspsnippets.com/Articles/2945/ASPNet-MVC-Core-Hello-World-Tutorial-with-Sample-Program-example/";
        string description = "Here Mudassar Khan has provided a short Hello World Tutorial using a small Sample Program example on how to use and develop applications in ASP.Net MVC Core 2.1 for the first time.";
        string body = this.PopulateBody(name, title, url, description);
 
        //Read SMTP section from AppSettings.json.
        string host = this.Configuration.GetValue<string>("Smtp:Server");
        int port = this.Configuration.GetValue<int>("Smtp:Port");
        string fromAddress = this.Configuration.GetValue<string>("Smtp:FromAddress");
        string userName = this.Configuration.GetValue<string>("Smtp:UserName");
        string password = this.Configuration.GetValue<string>("Smtp:Password");
        bool enableSsl = this.Configuration.GetValue<bool>("Smtp:EnableSsl");
        bool defaultCredentials = this.Configuration.GetValue<bool>("Smtp:DefaultCredentials");
 
        using (MailMessage mm = new MailMessage(fromAddress, "recepient@gmail.com"))
        {
            mm.Subject = "New article published!";
            mm.Body = body;
            mm.IsBodyHtml = true;
            using (SmtpClient smtp = new SmtpClient())
            {
                smtp.Host = host;
                smtp.EnableSsl = enableSsl;
                NetworkCredential networkCred = new NetworkCredential(userName, password);
                smtp.UseDefaultCredentials = defaultCredentials;
                smtp.Credentials = networkCred;
                smtp.Port = port;
                smtp.Send(mm);
            }
        }
        ViewBag.Message = "Email sent.";
        return View("Index");
    }
 
    private string PopulateBody(string name, string title, string url, string description)
    {
        string body = string.Empty;
        string path = Path.Combine(this.Environment.WebRootPath , "Template\\EmailTemplate.htm");
        using (StreamReader reader = new StreamReader(path))
        {
            body = reader.ReadToEnd();
        }
        body = body.Replace("{UserName}", name);
        body = body.Replace("{Title}", title);
        body = body.Replace("{Url}", url);
        body = body.Replace("{Description}", description);
        return body;
    }
}
 
 

View

The View consists of an HTML Form with following ASP.Net Tag Helpers attributes.
asp-action – Name of the Action. In this case the name is Index.
asp-controller – Name of the Controller. In this case the name is Home.
method – It specifies the Form Method i.e. GET or POST. In this case it will be set to POST.
The Form consists of a Submit Button, when the Button is clicked the form is submitted.
Finally, the ViewBag object is checked for NULL and if it is not NULL then the value of the object is displayed using JavaScript Alert Message Box.
@addTagHelper*, Microsoft.AspNetCore.Mvc.TagHelpers
@{
    Layout = null;
}
 
<!DOCTYPE html>
 
<html>
<head>
    <meta name="viewport" content="width=device-width" />
    <title>Index</title>
</head>
<body>
    <form method="post" asp-controller="Home" asp-action="SendEmail">
        <input type="submit" value="Send" />
    </form>
    @if (ViewBag.Message != null)
    {
        <script type="text/javascript">
            window.onload = function () {
                alert("@ViewBag.Message");
            }
        </script>
    }
</body>
</html>
 
 

Possible Errors

The following error occurs when you try to send email using Gmail credentials in your application.
The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.Net.Mail.SmtpException: The SMTP server requires a secure connection or the client was not authenticated. The server response was: 5.5.1 Authentication Required. Learn more at
 

Solution

GMAIL Error: The SMTP server requires a secure connection or the client was not authenticated.
 
 

Screenshot

ASP.Net Core: Send Email using HTML Templates
 
 

Downloads

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