In this article I will explain with an example, how to send email with multiple attachments using
MailKit library in ASP.Net WebForms using C# and VB.Net.
Installing MailKit package
Mail Server Settings in Web.Config file
The following Mail Server settings need to be saved in the Web.Config file.
<system.net>
<mailSettings>
<smtp deliveryMethod="Network">
<network
host="smtp.gmail.com"
port="587" />
</smtp>
</mailSettings>
</system.net>
HTML Markup
The HTML Markup consists of following controls:
TextBox – For capturing the values of Recipient Email address, Subject, Body, Gmail account email address, Gmail account password.
FileUpload – For attaching multiple files as attachment to the email.
The FileUpload has been assigned with AllowMultiple attribute for multiple file selection.
Button – For sending email.
The Button has been assigned with an OnClick event handler.
<table border="0" cellpadding="0" cellspacing="0">
<tr>
<td style="width: 80px">To:</td>
<td><asp:TextBox ID="txtTo" runat="server"></asp:TextBox></td>
</tr>
<tr><td> </td></tr>
<tr>
<td>Subject:</td>
<td><asp:TextBox ID="txtSubject" runat="server"></asp:TextBox></td>
</tr>
<tr><td> </td></tr>
<tr>
<td valign="top">Body:</td>
<td><asp:TextBox ID="txtBody" runat="server" TextMode="MultiLine" Height="150" Width="200"></asp:TextBox></td>
</tr>
<tr><td> </td></tr>
<tr>
<td>File Attachment:</td>
<td><asp:FileUpload ID="fuAttachment" runat="server" AllowMultiple="true" /></td>
</tr>
<tr><td> </td></tr>
<tr>
<td>Gmail Email:</td>
<td><asp:TextBox ID="txtEmail" runat="server"></asp:TextBox></td>
</tr>
<tr><td> </td></tr>
<tr>
<td>Gmail Password:</td>
<td><asp:TextBox ID="txtPassword" runat="server" TextMode="Password"></asp:TextBox></td>
</tr>
<tr><td> </td></tr>
<tr>
<td></td>
<td><asp:Button Text="Send" OnClick="SendEmail" runat="server" /></td>
</tr>
</table>
Namespaces
You will need to import the following namespaces.
C#
using MimeKit;
using MailKit.Net.Smtp;
using System.IO;
using System.Configuration;
using System.Net.Configuration;
using MailKit.Security;
VB.Net
Imports MimeKit
Imports MailKit.Net.Smtp
Imports System.IO
Imports System.Configuration
Imports System.Net.Configuration
Imports MailKit.Security
Sending email with multiple attachments 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.
Sending Email using MailKit
When the SendEmail Button is clicked, the Recipient email address (to), the Sender email address (from), Subject, Body and Attachment details are fetched from their respective fields and are set into the respective properties of the object of the MimeMessage class.
Setting Body of Email
For Body and Attachments, 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 multiple Files
The FileUpload is checked for Attachments and if it has Files then a FOR EACH loop is executed over the posted Files and inside the loop each File is added as Attachment to the Builder 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 Web.Config file and are passed as parameter to the Connect method along with the SecureSocketOptions set to Auto.
Note: Setting
Auto allows
MailKit service to decide which
SSL or
TLS option to use. Hence, enabling
SSL is not required.
Also, the CheckCertificateRevocation is set to FALSE.
Note: This is optional and must be used only when Certificate errors are occurring.
And, the methods of the Mail Server such as
Connect,
Authenticate,
Send and
Disconnect are executed and a success message is displayed in
JavaScript Alert
MessageBox using
RegisterStartupScript method.
C#
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;
IList<HttpPostedFile> postedFiles = fuAttachment.PostedFiles;
//Read SMTP section from Web.Config.
SmtpSection smtpSection = (SmtpSection)ConfigurationManager.GetSection("system.net/mailSettings/smtp");
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()
{
TextBody = body
};
if (fuAttachment.HasFile)
{
foreach (HttpPostedFile postedFile in postedFiles)
{
string fileName = Path.GetFileName(postedFile.FileName);
builder.Attachments.Add(fileName, postedFile.InputStream);
}
}
mm.Body = builder.ToMessageBody();
using (SmtpClient smtp = new SmtpClient())
{
//Set to False to avoid Certificate verification.
smtp.CheckCertificateRevocation = false;
smtp.Connect(host, port, SecureSocketOptions.Auto);
smtp.Authenticate(from, password);
smtp.Send(mm);
smtp.Disconnect(true);
}
}
ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Email sent.');", true);
}
VB.Net
Protected Sub SendEmail(ByVal sender As Object, ByVal e As EventArgs)
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
Dim postedFiles As IList(Of HttpPostedFile) = fuAttachment.PostedFiles
'Read SMTP section from Web.Config.
Dim smtpSection As SmtpSection = CType(ConfigurationManager.GetSection("system.net/mailSettings/smtp"), 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() With {
.TextBody = body
}
If fuAttachment.HasFile Then
For Each postedFile As HttpPostedFile In postedFiles
Dim fileName As String = Path.GetFileName(postedFile.FileName)
builder.Attachments.Add(fileName, postedFile.InputStream)
Next
End If
mm.Body = builder.ToMessageBody()
Using smtp As SmtpClient = New SmtpClient()
'Set to False to avoid Certificate verification.
smtp.CheckCertificateRevocation = False
smtp.Connect(host, port, SecureSocketOptions.Auto)
smtp.Authenticate(from, password)
smtp.Send(mm)
smtp.Disconnect(True)
End Using
End Using
ClientScript.RegisterStartupScript(Me.GetType(), "alert", "alert('Email sent.');", True)
End Sub
Possible Errors
The possible errors (exceptions) occurring while sending email with
MailKit in .Net are covered in the following article.
Screenshots
Email Form
The received email
Downloads