Hi there @GVaughan 

Thanks for sharing your question with us! Happy to help! 

You hit the nail on the head by considering this situation would cause deliverability issues. Technically, leads that are even a year old would be categorized as ‘unengaged’ so I wouldn’t suggest having the first messages from your brand be sent to old leads as this would negatively impact your deliverability and not build a strong sender reputation with inbox providers. I would check out our deliverability best practices documentation to avoid hitting the spam with these practices. I also found a helpful thread on this exact topic to steer you in the right direction of how to engage these lapsed users. 

Any sender new to Klaviyo must warm up their sending infrastructure when moving to a new email service provider. So I would recommend following your normal warming protocols as you are a new sender and having your welcome flow send to new users just signing up to your client’s brand. However, once you’ve seen the brand have a steady deliverability performance, I would then consider sending batches of these old leads through a kind of ‘winback flow’ or re-engagement campaign to see who takes an action!

Hope this helps! 

-Taylor