u/khaledalameldin

I'll vibe code an ESP on top of SendGrid. This is insane.

A few weeks back, I was on a call with someone running CRM at a DTC brand. They'd run a real holdout test on their Klaviyo flows, split their active list 50/50, shut off all flow emails (welcome, browse, cart, checkout, post-purchase) to one half for an extended window, and kept the other half on everything as usual. Same source mix, same campaign cadence on top.

They went in expecting incrementality numbers across all five flows that would help build the internal case for more lifecycle investment. What came back: only the welcome series showed a statistically significant lift. Cart, browse, checkout, and post-purchase came back flat to slightly negative.

When they took it to Klaviyo's team, the read they got was that there were probably gaps in the flows themselves, with recommendations to tighten things up. Their team made the changes. The follow-up data has been pointing in the same direction.

Their honest takeaway wasn't that email is dead; their campaigns still move revenue cleanly. It's specifically the templated flow architecture that flattens at scale. They think the missing piece is personalization at the recipient level, but wiring that up in Klaviyo at audience scale means basically rebuilding segment logic from scratch, which they don't have the bandwidth for.

The thing I haven't stopped thinking about since the call: welcome is the only flow where the email is actually carrying information the recipient doesn't already have. They haven't seen your brand voice yet, don't know your range, don't know your story. Every other flow is reminding them of something they already know: they saw the product, they put it in cart, they started checkout. The email isn't adding signal at that point; it's just adding sends. So in a templated regime, welcome has something new to say, and the rest don't. That tracks with what their data showed.

Three questions for the sub:

• Has anyone run a real flow holdout (60+ days, statistically significant audience)? Did you welcome win and the rest go flat for you too, or did you see different patterns?
• For brands above 100k profiles, what % of your flow content is actually event-property-driven (using predicted_clv, expected_date_of_next_order, location, last category) vs. plain templated?
• If your flows DID show incremental lift in a holdout, what was the personalization layer actually doing differently from "the recipient already saw the product"?