Hi there @Dwilcox, 

Welcome to the Community! 

I’d check out these helpful resources before contacting old leads from a client so you don’t suffer possible poor deliverability consequences and warm this list before you send to them. 

https://community.klaviyo.com/analytics%2Dand%2Ddeliverability%2D72/i%2Dhave%2Da%2Dvery%2Dold%2Dlist%2Dthat%2Di%2Dhave%2Dnot%2Dsent%2Dto%2Din%2Da%2Dwhile%2Dhow%2Dcan%2Di%2Dstart%2Dsending%2Dto%2Dit%2Dagain%2D1740

If you’re considering adding a profile property to those who decide they want to be contacted and then grouping these leads into a segment, I’d suggest notifying your client of these leads who opt in in either two ways. You can:

1.  Give your client Klaviyo account access to see who responds to this resurgence campaign in the segment. 
2. Set up a segment-triggered flow of those who are adding into the segment and create a flow email notification that will send your client and email with the email of the client when you add a personalization variable to the email.

Thank you for participating in the Community!

-Taylor