Do you have any other data you’ve tracked with your contacts that sets them above a ‘cold’ lead?

Something like ‘Ordered in the Past 30 Days’ - that to me would be a great population to test the waters with for warming. They know your brand, won’t be surprised by an email, and ideally your warming emails have some great valuable content inside for them so that they are excited for the next warming email that might come their way after.

After you’ve established a few sends with this group (and it is going well!), start to trickle in your ‘not-sures’ for engagement but be thoughtful on pulling them out after a few sends are ignored. They can be re-engaged later when your Klaviyo account is really established and it isn’t as risky to keep them in your send list during this warming phase.

Hope this helps - it can be a complicated topic for sure, haha! 

Totally agree with @Spark Bridge Digital LLC - if you don’t have engagement data from a previous platform, you can leverage other data points (like recent purchases) as test population to start warming up the audience in Klaviyo.  As mentioned, recent purchasers is a strong segment to start with.

Another audience you can reference in Shopify is to export Customers within recent date ranges of the “Date added as customer.” (Shopify refers them as Customer even though they may not have purchased yet).  This would be a good contender for a second batch or follow on groups of folks to try warming up against.

At some point, you can trickle further “batches” of subscribers further and further back into different time ranges to test their engagement receptivity.  Make sure to send each “batch” as a separate Campaign so you can easily see their engagement analytics separately so you can adjust accordingly.  

Hope this helps!

I hope these article about infrastructure warmup helps

https://help.klaviyo.com/hc/en-us/articles/360025945671-Guide-to-Warming-Your-Sending-Infrastructure