Cors error missing allow origin header. MailKit

I have cors error missing allow origin header error only on ONE post request. My CORS Policy

public void ConfigureServices(IServiceCollection services)
        {
            services.AddCors(options =>
            {
                options.AddPolicy("AllowAllOrigins",
                      builder =>
                      {
                          builder.SetIsOriginAllowed(_ => true)
                                  .AllowAnyHeader()
                                  .AllowAnyMethod()
                                  .AllowCredentials();
                      });
            });
}

Every request work fine, but one POST request fails, it's really weird. Code in controller action which failed use MailKit and SMTP to send email, maybe that's cause