In this article I will explain how to send email asynchronously in background using Thread in ASP.Net.
The need of sending asynchronous email arises since email sending process takes significant amount of time to execute and to keep the users waiting until the email is being sent is not acceptable. Thus this article will explain how an email sending process can be executed in background Thread and thus removes the latency involved in the email sending process.
 
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.
<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>
 
Send email asynchronous email using background thread in ASP.Net
 
 
Namespaces
You will need to import the following namespaces
C#
using System.IO;
using System.Net;
using System.Net.Mail;
using System.Threading;
VB.Net
Imports System.IO
Imports System.Net
Imports System.Net.Mail
Imports System.Threading
 
 
 
Sending email asynchronously in background using Thread
Below is the code to send email using Gmail account and Gmail SMTP server in ASP.Net, the Recipient email address (to), the Sender email address (from), Subject and Body is fetched from their respective fields.
Then all these values are passed as parameter to SendEmail function.
For sending email asynchronously in background using Thread, we need to define a new Thread object and within which we will call the SendEmail function using delegate in C# and Sub in VB.Net.
Finally the Thread object’s IsBackground property is set to true (so that it executes as a background process) and the thread is started.
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.
 
Note: If you need to know more about sending emails from Gmail account and sending emails with attachment, please refer the following articles

C#
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);
    }
}
 
VB.Net
Protected Sub SendAsyncEmail(sender As Object, 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 postedFile As HttpPostedFile = fuAttachment.PostedFile
    Dim email As New Thread(Sub() SendEmail([to], from, password, subject, body, postedFile))
    email.IsBackground = True
    email.Start()
    ClientScript.RegisterStartupScript([GetType](), "alert", "alert('Email sent.');", True)
End Sub
 
Private Sub SendEmail([to] As String, from As String, password As String, subject As String, body As String, postedFile As HttpPostedFile)
    Using mm As New MailMessage(from, [to])
        mm.Subject = subject
        mm.Body = body
        If postedFile.ContentLength > 0 Then
            Dim fileName As String = Path.GetFileName(postedFile.FileName)
            mm.Attachments.Add(New Attachment(postedFile.InputStream, fileName))
        End If
        mm.IsBodyHtml = False
        Dim smtp As New SmtpClient()
        smtp.Host = "smtp.gmail.com"
        smtp.EnableSsl = True
        Dim NetworkCred As New NetworkCredential(from, password)
        smtp.UseDefaultCredentials = True
        smtp.Credentials = NetworkCred
        smtp.Port = 587
        smtp.Send(mm)
    End Using
End Sub
 
Send email asynchronous email using background thread in ASP.Net

Send email asynchronous email using background thread in ASP.Net
 
 
Downloads