In this article I will explain with an example, how to send email with attachment using MailKit in ASP.Net Core Razor Pages.
Note: For beginners in ASP.Net Core Razor Pages, please refer my article ASP.Net Core Razor Pages: Hello World Tutorial with Sample Program example.
 
 
Installing MailKit package
You will need to install the MailKit package, for details on installation please refer Install MailKit from Nuget in Visual Studio.
 
 
Mail Server Settings in AppSettings.json file
The Mail Server settings are saved in the Smtp section as shown below.
{
   "Smtp": {
      "Server": "smtp.gmail.com",
      "Port": 587
   }
}
 
 
MimeKit MimeMessage and MailKit SmtpClient class
MimeMessage class properties
Following are the required properties of the MimeMessage class.
From – Sender’s email address.
To – Recipient(s) Email Address.
CC – Carbon Copies. (If any)
BCC – Blind Carbon Copies. (If any)
Subject – Subject of the Email.
Body – Body of the Email.
Attachments – Attachments. (If any)
ReplyTo – ReplyTo Email address.
 
SmtpClient class methods
Following are the methods of the SmtpClient class.
Connect – The connection to the SMTP Server is established using the domain and the port number.
Authenticate – The username and password of the SMTP Server is authenticated.
Send – The MimeMessage object is passed to it and the email is sent.
Disconnect – Disconnects the connection with SMTP Server.
 
 
Model
The Model class consists of the following properties.
Note: IFormFile is the new Class for Files in .Net Core. It is a replacement of HttpPostedFileBase class.
 
public class EmailModel
{
    public string To { get; set; }
    public string Subject { get; set; }
    public string Body { get; set; }
    public IFormFile Attachment { get; set; }
    public string Email { get; set; }
    public string Password { get; set; }
}
 
 
Namespaces
You will need to import the following namespaces.
using System.IO;
using MimeKit;
using MailKit.Net.Smtp;
using Microsoft.Extensions.Configuration;
 
 
Razor PageModel (Code-Behind)
The PageModel consists of following Handler methods.
Handler method for handling GET operation
This Handler method left empty as it is not required.
 
Handler method for handling POST operation
This Handler method handles the call made from the POST function from the Razor Page.
Note: For more details on how to use Model class object for capturing Form field values, please refer my article ASP.Net Core Razor Pages: Form Submit (Post) Example.
 
Inside this Action method, the posted values are captured through the EmailModel class object. All the fetched values are set into an object of the MailMessage class except the Body and Attachment.
Setting Body of Email
For Body and Attachment, an object of Builder class is created. The Body of the email is Text (Non HTML) hence it is set into the TextBody property of the Builder class object.
Attaching File
The IFormFile is checked for Attachment and if it has File then the posted File is added as Attachment to the Builder object.
Sending Email
Then, an object of the SmtpClient class is created and the Host and Port are fetched from the SMTP section of the AppSettings.json file and are set in Connect method and the methods.
And, the methods of the Mail Server such as Connect, Authenticate, Send and Disconnect are executed and a success message is set to a ViewData object.
public class IndexModel : PageModel
{
    public IConfiguration Configuration { get; set; }
    public EmailModel Model { get; set; }
 
    public IndexModel(IConfiguration _configuration)
    {
        this.Configuration = _configuration;
    }
 
    public void OnGet()
    {
    }
 
    public void OnPostSendEmail(EmailModel model)
    {
        //Read SMTP section from AppSettings.json.
        string host = this.Configuration.GetValue<string>("Smtp:Server");
        int port = this.Configuration.GetValue<int>("Smtp:Port");
 
        using (MimeMessage mm = new MimeMessage())
        {
            mm.From.Add(new MailboxAddress("Sender", model.Email));
            mm.To.Add(new MailboxAddress("Recepient", model.To));
            mm.Subject = model.Subject;
            BodyBuilder builder = new BodyBuilder();
            builder.TextBody = model.Body;
 
            //Check whether any Attachment is present and attach it.
            if (model.Attachment != null)
            {
                string fileName = Path.GetFileName(model.Attachment.FileName);
                builder.Attachments.Add(fileName, model.Attachment.OpenReadStream());
            }
            mm.Body = builder.ToMessageBody();
            using (SmtpClient smtp = new SmtpClient())
            {
                smtp.Connect(host, port);
                smtp.Authenticate(model.Email, model.Password);
                smtp.Send(mm);
                smtp.Disconnect(true);
            }
        }
        ViewData["Message"] = "Email sent.";
    }
}
 
 
Razor Page (HTML)
Inside the Razor Page, the ASP.Net TagHelpers is inherited.
The HTML of Razor Page consists of an HTML Form.
The Form has been specified with enctype=“multipart/form-data” attribute as it is necessary for File Upload operation
The Form consists of HTML TextBox, TextArea, FileUpload element and a Submit Button.
The Submit Button has been set with the POST Handler method using the asp-page-handler attribute.
Note: In the Razor PageModel, the Handler method name is OnPostSubmit but here it will be specified as Submit when calling from the Razor HTML Page.
 
When the Send Button is clicked, the Form gets submitted and the Model object is sent to the PageModel.
Finally, the ViewData object is checked for NULL and if it is not NULL then the value of the object is displayed using JavaScript Alert Message Box.
@page
@model Send_Email_Attachment_MailKit_Core_Razor.Pages.IndexModel
@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" enctype="multipart/form-data">
        <table>
            <tr>
                <td style="width: 80px">To:</td>
                <td><input type="text" asp-for="Model.To" /></td>
            </tr>
            <tr><td>&nbsp;</td></tr>
            <tr>
                <td>Subject:</td>
                <td><input type="text" asp-for="Model.Subject" /></td>
            </tr>
            <tr><td>&nbsp;</td></tr>
            <tr>
                <td valign="top">Body:</td>
                <td><textarea cols="20" rows="3" asp-for="Model.Body"></textarea></td>
            </tr>
            <tr><td>&nbsp;</td></tr>
            <tr>
                <td>File Attachment:</td>
                <td><input type="file" asp-for="Model.Attachment" /></td>
            </tr>
            <tr><td>&nbsp;</td></tr>
            <tr>
                <td>Gmail Email:</td>
                <td><input type="text" asp-for="Model.Email" /></td>
            </tr>
            <tr><td>&nbsp;</td></tr>
            <tr>
                <td>Gmail Password:</td>
                <td><input type="password" asp-for="Model.Password"/></td>
            </tr>
            <tr><td>&nbsp;</td></tr>
            <tr>
                <td></td>
                <td><input type="submit" value="Send" asp-page-handler="SendEmail" /></td>
            </tr>
        </table>
    </form>
    @if (ViewData["Message"] != null)
    {
        <script type="text/javascript">
            window.onload = function () {
                alert("@ViewData["Message"]");
            };
        </script>
    }
</body>
</html>
 
 
Possible Errors
The possible errors (exceptions) occurring while sending email with MailKit in .Net are covered in the following article.
Errors (Exceptions) while sending email with MailKit in .Net
 
 
Screenshot
Email Form
ASP.Net Core Razor Pages: Send Email with Attachment using MailKit
 
Received Email
ASP.Net Core Razor Pages: Send Email with Attachment using MailKit
 
 
Downloads
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