I am getting error while sending email "The specified string is not in the form required for an e-mail address." plz help me

string strConnection= System.Configuration.ConfigurationManager.ConnectionStrings["MyConnectionString"].ConnectionString;

       // string strSelect = "SELECT Username,password FROM registration WHERE emailid = @emailid";
        string strSelect = "SELECT name FROM registration WHERE email_id = @email_id";
 
         SqlConnection connection = new SqlConnection(strConnection);
        SqlCommand command = new SqlCommand();
        command.Connection = connection;
        command.CommandType = CommandType.Text;
        command.CommandText = strSelect;

        //SqlParameter email = new SqlParameter("@emailid", SqlDbType.NVarChar,100);
        SqlParameter email = new SqlParameter("@email_id", SqlDbType.VarChar, 100);
        email.Value = txtEmail.Text.Trim().ToString();
        command.Parameters.Add(email);
      
        DataSet dsPwd = new DataSet();
        SqlDataAdapter dAdapter = new SqlDataAdapter(command);
        connection.Open();
        dAdapter.Fill(dsPwd);
        connection.Close();
        if(dsPwd.Tables[0].Rows.Count > 0 )
        {
            MailMessage loginInfo = new MailMessage();
            //loginInfo.To.Add(txtEmail.Text.ToString());
            loginInfo.To.Add(new MailAddress(txtEmail.Text));
            loginInfo.From = new MailAddress("mail@gmail.com");
            loginInfo.Subject = "Forgot Password Information";
 
            loginInfo.Body = "Username: " + dsPwd.Tables[0].Rows[0]["Username"] + "<br><br>Password: " + dsPwd.Tables[0].Rows[0]["password"] + "<br><br>";
            loginInfo.IsBodyHtml = true;
            SmtpClient smtp = new SmtpClient();
            smtp.Host = "smtp.gmail.com";
            smtp.Port = 587;
            smtp.EnableSsl = true;
            smtp.Credentials = new System.Net.NetworkCredential("mymail@gmail.com", "password");
            smtp.Send(loginInfo);
            lblmsg.Text ="Password is sent to you email id,you can now Login";
        }
        else
        {
            lblmsg.Text = "Email Address Not Registered";
        }
    }