How to store list of file name into a single list and send it through email?

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C#3.0

C#

I've got an application that scan certain directories for any file which exceeds certain size. After it detects it, it will send a warning email, stating that certain files have reached certain size limits. My problem is my current program will send one email per file. Meaning if there is 10 file that is over limit, then it will will send 10 email. How to make it compile all of the file and send a list of those file in a single email?Here is my code if needed:

private void Form1_Load(object sender, EventArgs e)
        {
            count = 0;
            timer = new Timer();
            timer.Interval = 1000;
            timer.Tick += new EventHandler(timer1_Tick);
            timer.Start();
            

            List<string> s1 = System.IO.Directory.GetFiles(@"F:\gdimaging\data", "*.*", SearchOption.AllDirectories).ToList<string>();
            s1.AddRange(System.IO.Directory.GetFiles(@"F:\hios\DATA", "*.*", SearchOption.AllDirectories).ToList<string>());
            s1.AddRange(System.IO.Directory.GetFiles(@"F:\imgviewer\data", "*.*", SearchOption.AllDirectories).ToList<string>());
            s1.AddRange(System.IO.Directory.GetFiles(@"F:\newcnas\data", "*.*", SearchOption.AllDirectories).ToList<string>());
            s1.AddRange(System.IO.Directory.GetFiles(@"F:\newpod\data", "*.*", SearchOption.AllDirectories).ToList<string>());
            s1.AddRange(System.IO.Directory.GetFiles(@"F:\OMS\data", "*.*", SearchOption.AllDirectories).ToList<string>());
            s1.AddRange(System.IO.Directory.GetFiles(@"F:\WEBIMG", "*.*", SearchOption.AllDirectories).ToList<string>());
                     
            //s1 = Directory.GetFiles(@"F:\gdimaging\data", "*.*");
            dt.Columns.Add("File_Name");
            dt.Columns.Add("File_Type");
            dt.Columns.Add("File_Size");
            dt.Columns.Add("Create_Date");
            foreach(string s in s1)
            {
                try
                {
                    FileInfo info = new FileInfo(s);
                    FileSystemInfo sysInfo = new FileInfo(s);
                    dr = dt.NewRow();
                    //System.Collections.Generic.List<string> nameList;
                    dr["File_Name"] = sysInfo.Name;
                    dr["File_Type"] = sysInfo.Extension;
                    dr["File_Size"] = (info.Length / 1024).ToString();
                    dr["Create_Date"] = sysInfo.CreationTime.Date.ToString("dd/MM/yyyy");
                    dt.Rows.Add(dr);

                    
                    if ((info.Length / 1024) > 1500000)
                    {
                        //ArrayList exceed = new ArrayList();
                        //exceed.Add(sysInfo.Name).ToString();
                        //MessageBox.Show("" + sysInfo.Name + " HAS REACH IT SIZE LIMIT!!");
                        ///Basic Email message 
                        MailMessage mailMessage = new MailMessage();
                        // Email to send to
                        mailMessage.To.Add(new MailAddress("shahrul1509@yahoo.com"));
                        mailMessage.To.Add(new MailAddress("shahrul_kakashi90@hotmail.com"));
                        //MailAddress toEmail2 = new MailAddress("");
                        //mailMessage.To.Add(toEmail);
                        // set subject
                        mailMessage.Subject = "FILE SIZE WARNING MESSAGE";
                        // set body
                        mailMessage.Body = sysInfo.Name+ "HAS REACH ITS SIZE LIMIT.";
                        mailMessage.IsBodyHtml = true;
                        mailMessage.From = new MailAddress("**********", "Shahrul Nizam");
                        // Identify the credentials to login to the gmail account  
                        string sendEmailsFrom = "*********";
                        string sendEmailsFromPassword = "**********";
                        NetworkCredential cred = new NetworkCredential(sendEmailsFrom, sendEmailsFromPassword);
                        SmtpClient mailClient = new SmtpClient("smtp.gmail.com", 587);
                        mailClient.EnableSsl = true;
                        mailClient.DeliveryMethod = SmtpDeliveryMethod.Network;
                        mailClient.UseDefaultCredentials = false;
                        mailClient.Timeout = 20000;
                        mailClient.Credentials = cred;
                        mailClient.Send(mailMessage);
                        MessageBox.Show("Email Notification Sent!");
                    }

                    if (dt.Rows.Count > 0)
                    {
                        dataGridView1.DataSource = dt;
                    }
                }
                catch (UnauthorizedAccessException ex)
                {
                    MessageBox.Show("Error : " + ex.Message);
                    continue;
                }
                
            }
        }