In this article I will explain with an example, how to send email in ASP.Net using C# and VB.Net.
The SMTP Mail settings are stored in the mailSettings sub-section of the section of the Web.Config file.
The SmtpSection class of the System.Net.Configuration namespace is used to read the SMTP Mail settings from Web.Config file in ASP.Net using C# and VB.Net.
HTML Markup
The HTML Markup consists of:
TextBox – For capturing the values of Recipient Email address, Subject and Body for the email
Button – For sending email.
The Button has been assigned OnClick event handler.
<table border="0" cellpadding="0" cellspacing="0">
        <td><asp:TextBox ID="txtTo" runat="server" /></td>
        <td><asp:TextBox ID="txtSubject" runat="server" /></td>
        <td valign = "top">Body:</td>
        <td><asp:TextBox ID="txtBody" runat="server" TextMode="MultiLine" Height="150" Width="200" /></td>
        <td><asp:Button ID="btnSend" Text="Send" runat="server" OnClick = "SendEmail" /></td>
Mail Server Settings in Web.Config file
Following are the Mail Server settings in the Web.Config file.
        <smtp deliveryMethod="Network" from="">
You will need to import the following namespaces.
using System.Net;
using System.Net.Mail;
using System.Configuration;
using System.Net.Configuration;
Imports System.Net
Imports System.Net.Mail
Imports System.Configuration
Imports System.Net.Configuration
Sending Email in ASP.Net
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:
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)
Port – Port Number of the SMTP server. (Gmail: 587)
When the Send Button is clicked, the Sender’s email address (from) is fetched from the SmtpSection of the Web.Config file, the Subject and Body are fetched from their respective TextBoxes and all these values are set into an object of the MailMessage class.
Then an object of the SmtpClient class is created and the settings of the Mail Server such has Host, Port, DefaultCredentials, EnableSsl, are fetched from the mailSettings section of the Web.Config file and are set in respective properties of the SmtpClient class object.
And Usename and Password values are passed as parameter to NetworkCredential class from their respective fields.
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)
    SmtpSection smtpSection = (SmtpSection)ConfigurationManager.GetSection("");
    using (MailMessage mm = new MailMessage(smtpSection.From, txtTo.Text.Trim()))
        mm.Subject = txtSubject.Text.Trim();
        mm.Body = txtBody.Text.Trim();
        mm.IsBodyHtml = false;
        using (SmtpClient smtp = new SmtpClient())
            smtp.Host = smtpSection.Network.Host;
            smtp.EnableSsl = smtpSection.Network.EnableSsl;
            NetworkCredential networkCred = new NetworkCredential(smtpSection.Network.UserName, smtpSection.Network.Password);
            smtp.UseDefaultCredentials = smtpSection.Network.DefaultCredentials;
            smtp.Credentials = networkCred;
            smtp.Port = smtpSection.Network.Port;
            ClientScript.RegisterStartupScript(this.GetType(), "alert", "alert('Email sent.');", true);
Protected Sub SendEmail(ByVal sender As Object, ByVal e As EventArgs)
    Dim smtpSection As SmtpSection = CType(ConfigurationManager.GetSection(""), SmtpSection)
    Using mm As MailMessage = New MailMessage(smtpSection.From, txtTo.Text.Trim())
        mm.Subject = txtSubject.Text.Trim()
        mm.Body = txtBody.Text.Trim()
        mm.IsBodyHtml = False
        Using smtp As SmtpClient = New SmtpClient()
            smtp.Host = smtpSection.Network.Host
            smtp.EnableSsl = smtpSection.Network.EnableSsl
            Dim networkCred As NetworkCredential = New NetworkCredential(smtpSection.Network.UserName, smtpSection.Network.Password)
            smtp.UseDefaultCredentials = smtpSection.Network.DefaultCredentials
            smtp.Credentials = networkCred
            smtp.Port = smtpSection.Network.Port
            ClientScript.RegisterStartupScript(Me.GetType(), "alert", "alert('Email sent.');", True)
        End Using
    End Using
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
Email Form
Send Email with example in ASP.Net using C# and VB.Net
Received Email
Send Email with example in ASP.Net using C# and VB.Net