Why error - Cannot implicitly convert type 'string' to 'System.Net.Mail.MailAddress'

Cannot implicitly convert type 'string' to 'System.Net.Mail.MailAddress' in the line message.From = textBox1.Text;

private void button29_Click(object sender, EventArgs e)
       {
           // System.Web.Mail.SmtpMail.SmtpServer is obsolete in 2.0
           // System.Net.Mail.SmtpClient is the alternate class for this in 2.0

           SmtpClient smtpClient = new SmtpClient();
           MailMessage message = new MailMessage();

           try
           {
               MailAddress fromAddress = new MailAddress(textBox1.Text, textBox2.Text);

               // You can specify the host name or ipaddress of your server
               // Default in IIS will be localhost
               smtpClient.Host = "gmail.com";

               //Default port will be 25
               smtpClient.Port = 25;

               //From address will be given as a MailAddress Object
               message.From = textBox1.Text;

               // To address collection of MailAddress
               message.To.Add("contact@kamnatrust.com");
               message.Subject = "Feedback";

               // CC and BCC optional
               // MailAddressCollection class is used to send the email to various users
               // You can specify Address as new MailAddress("admin1@yoursite.com")
               //message.CC.Add("admin1@yoursite.com");
               //message.CC.Add("admin2@yoursite.com");

               // You can specify Address directly as string
               // message.Bcc.Add(new MailAddress("admin3@yoursite.com"));
               // message.Bcc.Add(new MailAddress("admin4@yoursite.com"));

               //Body can be Html or text format
               //Specify true if it  is html message
               message.IsBodyHtml = false;

               // Message body content
               message.Body =richTextBox1.Text;

               // Send SMTP mail
               smtpClient.Send(message);

               label1.Text = "Email successfully sent.";
           }
           catch (Exception ex)
           {
               label1.Text= "Send Email Failed." + ex.Message;
           }
       }