What’s the difference between full migration and split delivery?

When you're switching ESPs, you've got two different end-states to choose from. Not just two migration styles, but two different ways of running email long-term. Understanding the distinction before you start will save you a lot of rework.

Full migration means you're moving everything to one new ESP and eventually switching off the old one. You might run both in parallel for a few weeks during the transition period, but the goal is a clean cut. One vendor, one dashboard, one place to look when something breaks.

Split delivery is a permanent setup where different types of email live on different platforms. Your transactional email (receipts, password resets, shipping notifications) goes through one provider, and your marketing campaigns go through another. The split isn't a stepping stone. It's the destination.

A common pairing: Postmark for transactional and Klaviyo for marketing. Or Twilio SendGrid for triggered sends and Mailchimp for newsletters. The exact combination depends on your priorities.

And the main reason to go split delivery is stream separation. If a marketing campaign triggers a spike in spam complaints, that reputational hit stays contained to your marketing stream. Your password reset emails keep flowing without interruption. That separation genuinely matters when you're sending both types at volume.

Full migration wins on simplicity. One contract, one set of integrations, all your subscriber data in one place. For smaller senders or teams without dedicated deliverability resources, managing two platforms adds overhead that rarely pays off.

Here's a rough guide for choosing:

• If transactional email is critical to your product and you send serious marketing volume, split delivery is worth the complexity.
• If you're a smaller sender, just getting started, or want one clean system, full migration is the right call.
• Some teams start with a full migration and later carve out a separate transactional stream once they hit the volume where it matters. That's a perfectly reasonable path. (Just make sure you plan for it before you pick your first new ESP.)

Not sure which setup fits your situation? Our SOS hotline is free and we'll talk through the specifics with you, no pitch involved.