What actually breaks when you switch platforms?
Almost nothing breaks in your data. Contacts, custom fields, templates, and engagement history export to CSV or JSON, and any competent platform imports them. What breaks is your sender reputation. Mailbox providers score the domain and IP you send from, and a new platform usually means a new sending identity with no track record. Blast your whole list from a cold domain on day one and a large share lands in spam. The data is a copy job; deliverability is the part that needs a plan.
Export everything before you cancel anything
The cheapest insurance in a migration is timing. Export a complete copy of your data while the old account is still live and paid, then keep it read-only until the new platform is proven. Cancel first and you may lose access to unsubscribe records or engagement history you cannot rebuild.
- Contacts with every custom field — not just name and email, but the attributes your segments depend on.
- Unsubscribes and the full suppression list — hard bounces, complaints, and manual blocks.
- Templates and reusable content, plus the automations and journeys you will recreate.
- Event history and engagement data — opens, clicks, and the behavioral events your triggers fire on.
- DNS and authentication records — your current SPF, DKIM, and DMARC setup, for reference.
Store the export somewhere you control, not just inside the new vendor. Owning a clean copy of your own data is the point of the whole exercise — see own your customer data for why that copy matters beyond this migration.
Why carry the suppression list on every migration?
The suppression list — everyone who unsubscribed, hard-bounced, or filed a complaint — is the one export you can never skip. Legally, an unsubscribe is permanent and follows the person, not the platform; mailing them from a new tool is the same violation it was on the old one. For deliverability, those addresses are exactly the ones that generate complaints and bounces, the two signals that sink a cold domain fastest. Import the suppression list before you import anything else, and confirm the new platform treats it as an active block, not a historical note.
Re-permissioning: keep consent or re-confirm?
Consent is not tied to your old vendor, so in most cases it travels with the contact — a valid opt-in stays valid after a migration. You keep it when you can prove how and when each person subscribed and you keep sending the mail they agreed to. You re-confirm when provenance is missing, when the list is old and unengaged, or when you are changing what you send materially. A double opt-in re-permission campaign is the clean way to refresh a shaky list before it can hurt the new domain.
| Situation | Consent status | Action |
|---|---|---|
| Documented opt-in, recent engagement | Transfers | Import and mail as usual |
| Opt-in you can prove, same content | Transfers | Import; warm up gradually |
| No record of how they subscribed | Unclear | Re-confirm before mailing |
| Old, unengaged, or bought list | Weak or none | Re-permission or suppress |
How do you warm up the new domain and IP?
Warming up means growing your volume slowly so mailbox providers build trust in the new sending identity. Google's sender guidelines are explicit: start with a low volume to engaged users and increase it over time, and avoid sudden spikes if you have no history of sending large volumes. Begin with the contacts most likely to open — recent, active subscribers — then widen the audience over days or weeks. Watch your spam-complaint rate closely; Google asks bulk senders to keep it under 0.10% and never let it reach 0.30%. If bounces or deferrals climb, slow the ramp until the error rate drops, then increase again. A dedicated IP takes longer to warm than a shared pool, so plan the schedule against whichever you chose.
How do you map profiles, events, and segments?
Every platform models customers a little differently, so budget time to translate yours. Line up your profile attributes with the new field names and types, map your tracked events one-to-one, and rebuild dynamic segments against the new schema. This is the moment to prune dead fields and stale events rather than copy the mess across — a clean tracking plan makes the new platform's automations far easier to build. Keep transactional and marketing email on separate streams while you map, so a receipt never waits on a marketing warm-up and a broken segment never blocks a password reset.
What does a safe cut-over look like?
Do not flip a switch. Run both platforms in parallel and move traffic in stages — a small, engaged slice first, then larger segments as the numbers hold. Watch bounce rate, complaint rate, and inbox placement on the new tool after each increase; if any spike, pause and diagnose before sending more. Keep transactional mail on the proven path until the marketing streams are stable. Once the new platform carries your full volume cleanly for a couple of cycles, retire the old one. If you are still choosing a destination, our roundups of open-source marketing automation tools, Customer.io alternatives, and customer engagement platforms for startups are the place to start.