In this article I will explain with an example, how to send email with attachment in ASP.Net using C# and VB.Net.
 
 

HTML Markup

The following HTML Markup consists of:
TextBox – For capturing the values of Recipient Email address, Subject, Body, Gmail account email address, Gmail account password.
FileUpload – For attaching file to the email.
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 runat="server" ID="txtTo"></asp:TextBox></td>
    </tr>
    <tr>
        <td>&nbsp;</td>
    </tr>
    <tr>
        <td>Subject:</td>
        <td><asp:TextBox runat="server" ID="txtSubject"></asp:TextBox></td>
    </tr>
    <tr>
        <td>&nbsp;</td>
    </tr>
    <tr>
        <td valign="top">Body:</td>
        <td><asp:TextBox runat="server" ID="txtBody" TextMode="MultiLine" Height="150" Width="200"></asp:TextBox></td>
    </tr>
    <tr>
        <td>&nbsp;</td>
    </tr>
    <tr>
        <td>File Attachment:</td>
        <td><asp:FileUpload runat="server" ID="fuAttachment" /></td>
    </tr>
    <tr>
        <td>&nbsp;</td>
    </tr>
    <tr>
        <td>Gmail Email:</td>
        <td><asp:TextBox runat="server" ID="txtEmail"></asp:TextBox></td>
    </tr>
    <tr>
        <td>&nbsp;</td>
    </tr>
    <tr>
        <td>Gmail Password:</td>
        <td><asp:TextBox runat="server" ID="txtPassword" TextMode="Password"></asp:TextBox></td>
    </tr>
    <tr>
        <td>&nbsp;</td>
    </tr>
    <tr>
        <td></td>
        <td><asp:Button runat="server" ID="btnSend" Text="Send" OnClick="SendEmail" /></td>
    </tr>
</table>
 
 

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" 
               enableSsl="true"
               defaultCredentials="true"/>
        </smtp>
    </mailSettings>
</system.net>
 
 

Namespaces

You will need to import the following namespaces.
C#
using System.IO;
using System.Net;
using System.Net.Mail;
using System.Configuration;
using System.Net.Configuration;
 
VB.Net
Imports System.IO
Imports System.Net
Imports System.Net.Mail
Imports System.Configuration
Imports System.Net.Configuration
 
 

Sending email with attachment using Gmail SMTP Account

MailMessage Class Properties

Following are the required properties of the MailMessage 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
IsBodyHtml – Specify whether body contains text or HTML mark up.
Attachments – Attachments (if any)
ReplyTo – ReplyTo Email address.
 

SMTP Class Properties

Following are the properties of the SMTP class.
Host – SMTP Server URL (Gmail: smtp.gmail.com)
EnableSsl – Specify whether your host accepts SSL Connections (Gmail: True)
UseDefaultCredentials – Set to True in order to allow authentication based on the Credentials of to Account used to send emails
Credentials – Valid login credentials for the SMTP server (Gmail: email address and password)
Port – Port Number of the SMTP sever (Gmail: 587)
 
When 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 set into an object of the MailMessage class.
If the FileUpload control has attachment then, the attachment is added to the Attachments List of the MailMessage object.
Then, object of the SmtpClient class is created and the settings of the Mail Server such has Host, Port, DefaultCredentials and EnableSsl are fetched from the mailSettings section of the Web.Config file and are set in respective properties of the SmtpClient class object.
And Username and Password values are passed as parameter to NetworkCredential class from their respective fields.
Note: It is necessary to use the sender’s email address credentials while defining the Gmail SMTP Server Credentials as Gmail the sender’s email address must be equal to Gmail Username specified in credentials.
 
Finally, the email is being sent and success the message is displayed in JavaScript Alert Message Box using RegisterStartupScript method.
C#
protected void SendEmail(object sender, EventArgs e)
{
    //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;
    bool enableSsl = smtpSection.Network.EnableSsl;
    bool defaultCredentials = smtpSection.Network.DefaultCredentials;
 
    using (MailMessage mm = new MailMessage(txtEmail.Text, txtTo.Text))
    {
        mm.Subject = txtSubject.Text;
        mm.Body = txtBody.Text;
        mm.IsBodyHtml = false;
        if (fuAttachment.HasFile)
        {
            string fileName = Path.GetFileName(fuAttachment.PostedFile.FileName);
            mm.Attachments.Add(new Attachment(fuAttachment.PostedFile.InputStream, fileName));
        }
        using (SmtpClient smtp = new SmtpClient())
        {
            smtp.Host = host;
            smtp.Port = port;
            smtp.EnableSsl = enableSsl;
            smtp.UseDefaultCredentials = defaultCredentials;
            NetworkCredential networkCred = new NetworkCredential(txtEmail.Text, txtPassword.Text);
            smtp.Credentials = networkCred;
            smtp.Send(mm);
        }
    }
    ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Email sent.');", true);
}
 
VB.Net
Protected Sub SendEmail(ByVal sender As Object, ByVal e As EventArgs)
    '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
    Dim enableSsl As Boolean = smtpSection.Network.EnableSsl
    Dim defaultCredentials As Boolean = smtpSection.Network.DefaultCredentials
 
    Using mm As MailMessage = New MailMessage(txtEmail.Text,txtTo.Text)
        mm.Subject = txtSubject.Text
        mm.Body = txtBody.Text
        mm.IsBodyHtml = False
        If fuAttachment.HasFile Then
            Dim fileName As String = Path.GetFileName(fuAttachment.PostedFile.FileName)
            mm.Attachments.Add(New Attachment(fuAttachment.PostedFile.InputStream, fileName))
        End If
        Using smtp As SmtpClient = New SmtpClient()
            smtp.Host = host
            smtp.Port = port
            smtp.EnableSsl = enableSsl
            smtp.UseDefaultCredentials = defaultCredentials
            Dim networkCred As NetworkCredential = New NetworkCredential(txtEmail.Text, txtPassword.Text)
            smtp.Credentials = networkCred
            smtp.Send(mm)
        End Using
    End Using
    ClientScript.RegisterStartupScript(Me.GetType(), "alert", "alert('Email sent.');", True)
End Sub
 
 

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
 
 

Screenshots

Email Form

How to send email with attachment in ASP.Net
 

Received Email

How to send email with attachment in ASP.Net
 
 

Downloads

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