In this article I will explain with an example, how to send emails using GMAIL Account Credentials and also make use of threading to improve performance in ASP.Net using C#.
 
 
HTML Markup
The HTML Markup has a form with some fields such as Recipient Email address, Subject, Body, Attachment, Gmail account email address, Gmail account password and a Button to send the asynchronous email.
The Button has been assigned 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>
            &nbsp;
        </td>
    </tr>
    <tr>
        <td>
            Subject:
        </td>
        <td>
            <asp:TextBox ID="txtSubject" runat="server"></asp:TextBox>
        </td>
    </tr>
    <tr>
        <td>
            &nbsp;
        </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>
            &nbsp;
        </td>
    </tr>
    <tr>
        <td>
            File Attachment:
        </td>
        <td>
            <asp:FileUpload ID="fuAttachment" runat="server" />
        </td>
    </tr>
    <tr>
        <td>
            &nbsp;
        </td>
    </tr>
    <tr>
        <td>
            Gmail Email:
        </td>
        <td>
            <asp:TextBox ID="txtEmail" runat="server"></asp:TextBox>
        </td>
    </tr>
    <tr>
        <td>
            &nbsp;
        </td>
    </tr>
    <tr>
        <td>
            Gmail Password:
        </td>
        <td>
            <asp:TextBox ID="txtPassword" runat="server" TextMode="Password"></asp:TextBox>
        </td>
    </tr>
    <tr>
        <td>
            &nbsp;
        </td>
    </tr>
    <tr>
        <td>
        </td>
        <td>
            <asp:Button Text="Send" OnClick="SendAsyncEmail" runat="server" />
        </td>
    </tr>
</table>
 
 
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 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)
 
 
Namespaces
You will need to import the following namespaces.
using System.IO;
using System.Net;
using System.Net.Mail;
using System.Threading;
 
 
Sending Email using GMAIL in ASP.Net using Thread
When the Send Button is clicked, the Recipient email address (to), the Sender email address (from), Subject and Body are fetched from their respective fields.
Then all these values are passed as parameter to SendEmail function.
For sending email asynchronously in background using Thread, a new Thread object is defined and within which the SendEmail function is called using delegate in C# and Sub in VB.Net.
Inside the SendEmail function all these parameters 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, Username and Password are set to the SmtpClient class object.
Finally, the Thread object’s IsBackground property is set to true (so that it executes as a background process) and the thread is started and a Success message is displayed using JavaScript Alert Message Box.
Note: Using this technique has a drawback, since we are making use of a new Thread it becomes impossible to detect the final status of the email, i.e. whether the email has been sent successfully or failed. To overcome this problem, my suggestion would be to implement some logging mechanism that will be update the final status of the email.
 
protected void SendAsyncEmail(object sender, EventArgs e)
{
    string to = txtTo.Text;
    string from = txtEmail.Text;
    string password = txtPassword.Text;
    string subject = txtSubject.Text;
    string body = txtBody.Text;
    HttpPostedFile postedFile = fuAttachment.PostedFile;
    Thread email = new Thread(delegate()
    {
        SendEmail(to, from, password, subject, body, postedFile);
    });
 
    email.IsBackground = true;
    email.Start();
    ClientScript.RegisterStartupScript(GetType(), "alert""alert('Email sent.');"true);
}
 
private void SendEmail(string to, string from, string password, string subject, string body, HttpPostedFile postedFile)
{
    using (MailMessage mm = new MailMessage(from, to))
    {
        mm.Subject = subject;
        mm.Body = body;
        if (postedFile.ContentLength > 0)
        {
            string fileName = Path.GetFileName(postedFile.FileName);
            mm.Attachments.Add(new Attachment(postedFile.InputStream, fileName));
        }
        mm.IsBodyHtml = false;
        SmtpClient smtp = new SmtpClient();
        smtp.Host = "smtp.gmail.com";
        smtp.EnableSsl = true;
        NetworkCredential NetworkCred = new NetworkCredential(from, password);
        smtp.UseDefaultCredentials = true;
        smtp.Credentials = NetworkCred;
        smtp.Port = 587;
        smtp.Send(mm);
    }
}
 
 
Screenshots
Email Form
Send Email using GMAIL in ASP.Net using C#

Received Email
Send Email using GMAIL in ASP.Net using C#
 
 
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