In this article I will explain with an example, how to send email using MailKit library in Windows Forms (WinForms) Application using C# and VB.Net.

Installing MailKit package

You will need to install the MailKit package, for details on installation please refer Install MailKit from Nuget in Visual Studio.

Form Design

The following Form consists of:
TextBox – For capturing the values of Recipient Email address, Subject, Body, Gmail account, email address and Gmail account password.
Button – For sending email.
The Button has been assigned with the Click event handler.
Send Email using MailKit in Windows Forms

Mail Server Settings in App.Config file

The following Mail Server settings need to be saved in the App.Config file.
    <smtp deliveryMethod="Network">
          port="587" />


You will need to import the following namespaces.
using MimeKit;
using MailKit.Net.Smtp;
using System.Configuration;
using System.Net.Configuration;
Imports MimeKit
Imports MailKit.Net.Smtp
Imports System.Configuration
Imports System.Net.Configuration

Sending email using MailKit

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.
When the Send Button is clicked, the Recipient email address (to), the Sender email address (from), Subject and Body values are fetched from their respective fields and are passed as parameter to SendEmail function.
Inside the SendEmail function all these parameters are set into an object of the MimeMessage class.

Setting Body of Email

For Body, 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.

Sending Email

Then, an object of the SmtpClient class is created and the values of Host and Port are fetched from the SMTP section of the App.Config file and are passed as parameter to the Connect method.
Note:For more details on reading value from App.Config, please refer my article, Read AppSettings value from App.Config file using C# and VB.Net.
Finally, the methods of the Mail Server such as ConnectAuthenticateSend and Disconnect are executed and a success message is displayed using Message Box.
protected void SendEmail(object sender, EventArgs e)
    string to = txtTo.Text;
    string from = txtEmail.Text;
    string password = txtPassword.Text;
    string subject = txtSubject.Text;
    string body = txtBody.Text;
    //Read SMTP section from Web.Config.
    SmtpSection smtpSection = (SmtpSection)ConfigurationManager.GetSection("");
    string host = smtpSection.Network.Host;
    int port = smtpSection.Network.Port;
    using (MimeMessage mm = new MimeMessage())
        mm.From.Add(new MailboxAddress("Sender", from));
        mm.To.Add(new MailboxAddress("Recepient", to));
        mm.Subject = subject;
        BodyBuilder builder = new BodyBuilder();
        builder.TextBody = body;
        mm.Body = builder.ToMessageBody();
        using (SmtpClient smtp = new SmtpClient())
            smtp.Connect(host, port);
            smtp.Authenticate(from, password);
    MessageBox.Show("Email sent.");
Private Sub SendEmail(ByVal sender As Object, ByVal e As EventArgs) Handles btnSend.Click
    Dim [to] As String = txtTo.Text
    Dim from As String = txtEmail.Text
    Dim password As String = txtPassword.Text
    Dim subject As String = txtSubject.Text
    Dim body As String = txtBody.Text
    'Read SMTP section from Web.Config.
    Dim smtpSection As SmtpSection = CType(ConfigurationManager.GetSection(""), SmtpSection)
    Dim host As String = smtpSection.Network.Host
    Dim port As Integer = smtpSection.Network.Port
    Using mm As MimeMessage = New MimeMessage()
        mm.From.Add(New MailboxAddress("Sender", from))
        mm.To.Add(New MailboxAddress("Recepient", [to]))
        mm.Subject = subject
        Dim builder As BodyBuilder = New BodyBuilder()
        builder.TextBody = body
        mm.Body = builder.ToMessageBody()
        Using smtp As SmtpClient = New SmtpClient()
            smtp.Connect(host, port)
            smtp.Authenticate(from, password)
        End Using
    End Using
    MessageBox.Show("Email sent.")
End Sub

Possible Errors

The possible errors (exceptions) occurring while sending email with MailKit in .Net are covered in the following article.


Email Form
Send Email using MailKit in Windows Forms

The received email

Send Email using MailKit in Windows Forms