Welcome to the community @CapKirk 

Many factors determine whether an email is classified as spam by the receiving email system.

Have you set up your email authentication for SPF/DKIM/DMARC? This is a critical first step in email deliverability. If you have it configured correctly your https://www.klaviyo.com/settings/email/domains should look like my example below for your sending domain. Article on setting that up here: https://help.klaviyo.com/hc/en-us/articles/4402601857307 also a trouble-shooting guide on spam here: https://help.klaviyo.com/hc/en-us/articles/12034571748251 some of which will be relevant even if you’ve not yet started sending campaigns.

Also a fairly decent free spam testing tool for email content here: https://www.mail-tester.com/ though there are other more comprehensive paid tools e.g Litmus

Regarding your test recipients, are they hosted on the same email provider or different ones? This may indicate you’re having issues with one system in particular. 

It’s a frustrating issue, I know, so let me know how you get on.

Regards

Andy