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Send mail to multiple Users (Recipients) in ASP.Net using C# and VB.Net

I have added a button on click event of that button i am sending the emails.

HTML

<asp:Button Text="Send Bulk Email" runat="server" OnClick = "SendBulkEmail" />

Namespaces

using System.Net;
using System.Net.Mail;
using System.Data;
using System.Threading.Tasks;
using System.Configuration;
using System.Data.SqlClient;

C#

protected void SendBulkEmail(object sender, EventArgs e)
{
    DataTable dtUsers = new DataTable();
    string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
    using (SqlConnection conn = new SqlConnection(constr))
    {
        using (SqlCommand cmd = new SqlCommand("Users_GetEmails", conn))
        {
            cmd.CommandType = CommandType.StoredProcedure;
            using (SqlDataAdapter da = new SqlDataAdapter(cmd))
            {
                da.Fill(dtUsers);
                string subject = "Welcome Email";
                string body = "Hello {0},<br /><br />Welcome to ASPSnippets<br /><br />Thanks.";

                //Using Parallel Multi-Threading send multiple bulk email.
                Parallel.ForEach(dtUsers.AsEnumerable(), row =>
                {
                    SendEmail(row["Email"].ToString(), subject, string.Format(body, row["Name"]));
                });
            }
        }
    }
}

private bool SendEmail(string recipient, string subject, string body)
{
    MailMessage mm = new MailMessage("sender@gmail.com", recipient);
    mm.Subject = subject;
    mm.Body = body;
    mm.IsBodyHtml = true;
    SmtpClient smtp = new SmtpClient();
    smtp.Host = "smtp.gmail.com";
    smtp.EnableSsl = true;
    NetworkCredential NetworkCred = new NetworkCredential();
    NetworkCred.UserName = "sender@gmail.com";
    NetworkCred.Password = "<password>";
    smtp.UseDefaultCredentials = true;
    smtp.Credentials = NetworkCred;
    smtp.Port = 587;
    smtp.Send(mm);
    return true;
}

SQL

Table

CREATE TABLE [dbo].[Users](
	[UserId] [int] IDENTITY(1,1) NOT NULL,
	[Username] [nvarchar](20) NOT NULL,
	[Password] [nvarchar](20) NOT NULL,
	[Email] [nvarchar](30) NOT NULL,	
	
 CONSTRAINT [PK_Users] PRIMARY KEY CLUSTERED 
(
	[UserId] ASC
)WITH (PAD_INDEX  = OFF, STATISTICS_NORECOMPUTE  = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS  = ON, ALLOW_PAGE_LOCKS  = ON) ON [PRIMARY]
) ON [PRIMARY]

GO

Stored Procedure

-- Users_GetEmails 
CREATE PROCEDURE Users_GetEmails
	
AS
BEGIN	
	SET NOCOUNT ON;

	SELECT UserName, Email FROM Users
END
GO