Hi @phu, welcome to the community.

I believe Klaviyo uses a variety of domains/subdomains for click tracking where ctrk.klick2.com happens to be yours at the time.  Because many merchants share the same “domain” for click tracking, occasionally I see these get caught up in enterprise security filters.

If this continues to be a problem, you can also setup branded click tracking so it can be trk.yourdomain.com - it takes some time to setup and propagate and requires you to configure your DNS in your domain registrar depending on if you have dynamic branded sending domain or a static one. 

This will make all links originate to your domain for click tracking which can sometimes improve bypassing security filters.  Remember, your sending reputation (deliverability) still apply, so if you are linking to suspicious sites or have poor deliverability (you have poor engagement) you will still end up being filtered by security systems - that’s what they are designed to do.

If you want to set that up, can read more about that here:

• How to set up dedicated click tracking

Hope this helps!