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

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>
 
 

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 selecting file.
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>
 
 

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

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.
IsBodyHtml – Specify whether body contains text or HTML mark up.
Attachments – Attachments. (If any)
ReplyTo – ReplyTo Email address.
 

SmtpClient class methods

Following are the methods of the SMTP class.
Host – SMTP Server URL (Gmail: smtp.gmail.com)
Port – Port Number of the SMTP sever (Gmail: 587)
EnableSsl – Specify whether your host accepts SSL Connections (Gmail: True)
UseDefaultCredentials – Set to True in order to allow authentication based on the Credentials of the Account used to send emails
Credentials – Valid login credentials for the SMTP server (Gmail: email address and password)
 
 

Sending email with attachment using Gmail SMTP Account in ASP.Net

When Send Button is clicked, the Recipient email address (toAddress), the Sender email address (fromAddress), Subject, Body values are fetched from their respective fields and are set into an object of the MailMessage class.

Setting Body of Email

The Body of the email is Text (Non HTML) hence the IsBodyHtml property of MailMessage class is set to FALSE.

Attaching File

The FileUpload is checked for Attachment and if it has File then the File is added as Attachment to the MailMessage class object.

Sending Email

Then, an object of the SmtpClient class is created and the values of Host, Port, EnableSsl and UseDefaultCredentials are fetched from the SMTP section of the Web.Config file and set to the respective properties of SmtpClient class along with the Credentials.
Finally, the email is being sent and success the message is displayed in JavaScript Alert Message Box using RegisterStartupScript method.
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  = 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 Error

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

Send email using Gmail SMTP Mail Server in ASP.Net
 

Received Email

Send email using Gmail SMTP Mail Server in ASP.Net
 
 

Downloads