Sending to a list of contacts who have never consented to receive emails from your brand is never recommended. When you acquire a list through a third-party, you are not acquiring each individual email address owner’s consent. Sending to a list that was acquired from a third-party will result in elevated bounces, unsubscribes, and spam complaint rates.
Lastly, sending to a list that is acquired from a third party violates Klaviyo’s Acceptable Use Policy.