Platform Migration — email marketers

What a migration specialist actually does

An ESP migration touches everything at once: subscriber data and consent records, segments, template code, every automation, integrations with your store or CRM, and, most dangerously, your sending reputation. A migration specialist has run this project enough times to know where it goes wrong, and the deliverable is a cutover where revenue doesn't dip and mailbox providers don't notice anything suspicious.

The deliverability piece is the part teams underestimate. Mail from new infrastructure gets extra scrutiny from Gmail and Microsoft, so a specialist plans a warming schedule, starting with your most engaged segments at low volume and ramping over weeks, rather than pointing the full list at the new platform on day one. The common route is Mailchimp to Klaviyo for growing e-commerce brands, but the same discipline applies to any pair of platforms.

When to hire one

Hire before you sign the new contract, not after. A specialist can sanity-check the platform choice against your data model and flag costs the sales deck didn't mention, and their migration timeline should inform your contract overlap, since running two platforms for a month or two during warming is normal and cheaper than a botched hard cutover.

The other moment is mid-crisis: a migration someone started is half-done, flows are firing from both platforms or neither, and opens have cratered. That rescue work is common enough that specialists have a playbook for it too.

On timelines: a clean migration for a mid-sized program runs six to ten weeks end to end: two for data mapping and platform setup, two to four rebuilding flows and templates, and the rest warming the new infrastructure while the old platform winds down. Compressing the warming phase is the one shortcut that reliably backfires, so treat any quote promising a two-week full cutover as a red flag rather than a bargain.

What it costs

Migrations are fixed-scope projects. A straightforward move, list, core flows, a handful of templates, commonly runs $2,500–7,500; complex programs with custom integrations, large catalogs, or heavy automation libraries can reach $10,000–25,000. Quotes vary most on how many automations need rebuilding by hand, so an accurate flow inventory is the first thing a serious specialist will ask for.

Beware quotes that don't mention warming or a parallel-running period; a migration priced as a data-export exercise is how programs end up in the spam folder. The questions-to-ask guide has the full pre-hire checklist.