SMTP client StackOverflowException

我基本上创建了一个群发程序，问题是，如果我没有线程，它显然会冻结，它需要能够向用户显示进度。不使用另一个类/对象，它工作得很好。我得到一个stackoverflowexception:

{Cannot evaluate expression because the current thread is in a stack overflow state.}

this.numericUpDown1 = new System.Windows.Forms.NumericUpDown();

注意:这可能会误导，因为我甚至还没有创建线程，但它仍然得到stackoverflowexception。

这是代码:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Windows;
using System.Net.Mail;
namespace Mass_Mail
{
    public partial class Form1 : Form
    {
        Form2 frm = new Form2();
        Worker work = new Worker();
        public List<String> succed = new List<String>();
        public List<String> failed = new List<String>();
        public Form1()
        {
            InitializeComponent();
        }
        private void button2_Click(object sender, EventArgs e)
        {
            OpenFileDialog openFileDialog1 = new OpenFileDialog(); //Skapa och definiera openfiledialog
            openFileDialog1.InitialDirectory = Environment.GetFolderPath(Environment.SpecialFolder.Desktop); //sätt startmappen till skrivbordet
            openFileDialog1.Filter = "txt files (*.txt)|*.txt|All files (*.*)|*.*"; //textfiler.
            openFileDialog1.FilterIndex = 2;
            openFileDialog1.RestoreDirectory = true;
            if (openFileDialog1.ShowDialog() == DialogResult.OK)
            {
                try
                {

                        textBox1.Text = openFileDialog1.FileName.ToString();
                        using (StreamReader sr = new StreamReader(openFileDialog1.FileName)) {
                            String line;
                            while ((line = sr.ReadLine()) != null)
                            {
                                textBox2.AppendText(line + Environment.NewLine);
                            }
                }
                    }
             catch (Exception ex) {
                 MessageBox.Show("Kunde inte öppna  " + ex.Message);
             }
        }
}
        private void button1_Click(object sender, EventArgs e)
        {

        }

        private void button3_Click(object sender, EventArgs e)
        {
            frm.Show();
        }
        private void Form1_Load(object sender, EventArgs e)
        {
            frm.comboBox1.SelectedIndex = 0;
        }
        private void button4_Click(object sender, EventArgs e)
        {
           // work.sendmail(textBox6.Text);
        }

    }
    public class Worker
    {
        public void DoWork()
        {
            string[] lines = frm1.textBox2.Text.Split(new string[] { Environment.NewLine }, StringSplitOptions.None);
            for (int i = 0; i < lines.Length; i++)
            {
                sendmail(lines[i]);
            }
        }
        Form1 frm1 = new Form1();
        Form2 frm2 = new Form2();
        public void sendmail(String mail)
        {
            try
            {
                SmtpClient client = new SmtpClient(frm2.textBox1.Text, int.Parse(frm2.textBox2.Text));
                MailMessage msg = new MailMessage(frm1.textBox3.Text, mail);
                client.Timeout = decimal.ToInt32(frm2.numericUpDown1.Value);
                client.DeliveryMethod = SmtpDeliveryMethod.Network;
                client.UseDefaultCredentials = false;
                client.Credentials = new System.Net.NetworkCredential("", "");
                switch (frm2.comboBox1.SelectedIndex)
                {
                    case 0:
                        client.EnableSsl = true;
                        break;
                    case 1:
                        client.EnableSsl = false;
                        break;
                }
                msg.Subject = frm1.textBox4.Text;
                msg.Body = frm1.textBox5.Text;
                msg.BodyEncoding = UTF8Encoding.UTF8;
                msg.IsBodyHtml = true;
                client.Send(msg);
                frm1.succed.Add(mail);
                frm1.label6.Text = "Lyckades: " + frm1.succed.Count.ToString();
            }
            catch (System.Net.Mail.SmtpException ex)
            {
                MessageBox.Show("ERROR! " + ex);
                frm1.failed.Add(mail);
                frm1.label7.Text = "Misslyckades: " + frm1.failed.Count.ToString();
            }
            catch (System.FormatException e)
            {
                MessageBox.Show("ERROR! " + e);
                frm1.failed.Add(mail);
                frm1.label7.Text = "Misslyckades: " + frm1.failed.Count.ToString();
            }

        }
    }
}

我要创建一个DoWork线程。我从来没有做过这样的事情，而且我知道目前的代码非常糟糕。任何形式的帮助都是非常感激的。我对c#和多线程也很陌生。Form2只包含包含SMTP设置的文本框等，没有代码。

编辑:如果我不创建一个新对象

Worker work = new Worker();

它工作得很好!

Worker work = new Worker();

Form1 frm1 = new Form1();

Worker _worker;
public Form1()
{
    InitializeComponent();
    _worker = new Worker(this);
}

public class Worker
{
    Form1 _form1;
    public Worker(Form1 form1)
    {
        _form1 = form1;
    }
    ...