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 =>
                      builder =>
                          builder.SetIsOriginAllowed(_ => true)

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