I am trying to send email using smtp to multiple users from asp.net core web api with angular 2.0. but its throwing CORS error

Question

bellow is my error:

Access to XMLHttpRequest at 'https://localhost:44359/api/ClientCandidateBulkStatusUpdate' from origin 'http://localhost:4200' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.

I made settings in startup.cs like:

public void ConfigureServices(IServiceCollection services)
    {
        services.AddCors(options =>
        {
            options.AddPolicy("CorsPolicy",
                builder => builder.AllowAnyOrigin()
                .AllowAnyMethod()
                .AllowAnyHeader()
                // .SetIsOriginAllowed(origin => true)//allow any origin
                .AllowCredentials());
               // .Build());
                
        });
                    
        services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); 
    }

    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env)
    {
        if (env.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }
        else
        {
            app.UseHsts();
        }
        var builder = new ConfigurationBuilder()
        .SetBasePath(env.ContentRootPath)
        .AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
        .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true);

        builder.AddEnvironmentVariables();
        builder.Build();
        app.UseCors("CorsPolicy");
        ////app.UseCors(builder1 => builder1
        ////    .AllowAnyOrigin()
        ////    .AllowAnyMethod()
        ////    .AllowAnyHeader()
        ////    .SetIsOriginAllowed(origin => true)//allow any origin
        ////    .AllowCredentials());// allow credentials
        
        app.UseHttpsRedirection();
        app.UseMvc();
    }

I enabled CORS on Controller like

 [Route("api/[controller]")]
[ApiController]
[EnableCors("CorsPolicy")]
public class ClientCandidateBulkStatusUpdateController : ControllerBase
{}

my send mail code is:

public void Sendmail(String MailFrom, String Mailto, String Subject, String Body, String CC = "", Boolean Copy = false)
    {
        DataTable EmailSettingsDT = new DataTable();
        EmailSettingsDT = GetEmailSettings();
        if (EmailSettingsDT.Rows.Count > 0)
        {
            string a = EmailSettingsDT.Rows[0]["SMTPHost"].ToString();
            int port = Convert.ToInt32(EmailSettingsDT.Rows[0]["SMTPPort"]);
            using (SmtpClient smtp = new SmtpClient(EmailSettingsDT.Rows[0]["SMTPHost"].ToString()))
            {

                var basicCredential = new NetworkCredential(EmailSettingsDT.Rows[0]["SMTPUsername"].ToString(), EmailSettingsDT.Rows[0]["SMTPPassword"].ToString());
                smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
                smtp.EnableSsl = Convert.ToBoolean(EmailSettingsDT.Rows[0]["IS_SSL"].ToString());
                smtp.UseDefaultCredentials = false;
                smtp.Credentials = basicCredential;
                smtp.Port = Convert.ToInt32(EmailSettingsDT.Rows[0]["SMTPPort"].ToString());
                var mail = new MailMessage();
                mail.From = new MailAddress(EmailSettingsDT.Rows[0]["SMTPUsername"].ToString(), EmailSettingsDT.Rows[0]["DisplayName"].ToString());
                mail.To.Add(Mailto);
                if (Copy == true)
                {
                    mail.CC.Add(CC);

                }
                mail.IsBodyHtml = true;
                mail.Subject = Subject;
                mail.Body = Body;
                smtp.Send(mail);
                mail.Dispose();
                smtp.Dispose();
            }
            //var smtp = new SmtpClient(EmailSettingsDT.Rows[0]["SMTPHost"].ToString());

        }
    }
SMTP PORT:587, HOST:smtp.gmail.com

My angular code is:

UpdateClientReviewCandidateStatus(Data: any) {
const header = new Headers({ 'Content-type': 'application/json' });  
return this._http.post(this.apiUrl + 'ClientCandidateBulkStatusUpdate', Data, httpOptions).pipe(map((data: Response) => <any>data))

}

I tried with commented code also still not solved issue. SMTP is having limitation to send email for 100. I have not reached limit still it is throwing while sending bulk email. Some emails like 5 or 10 are sending but else get structed with above CORS error. I tried to send mail using MailKit and MailChimp also but no solution found. plz can anyone help me to solve this error.

thanks in advance.