How to switch ESPs without torching deliverability
A careful migration playbook — exporting data, warming domains, recreating flows, and avoiding the reputation cliff.
Switching email platforms is one of the riskiest operations in marketing because your sender reputation does not transfer. Do it carelessly and you land in spam on day one.
This playbook keeps the migration boring — which, for deliverability, is exactly what you want.
Before you move
Audit what you actually use: lists, segments, flows, templates, and integrations. Many migrations stall because no one mapped the flows.
Export contacts with consent status and engagement history. You will use engagement to decide who to migrate and who to suppress.
Pick the destination by your real constraint (see our tool comparisons). If creation speed is the issue, an AI-native tool like Brew can recreate on-brand templates fast; if it is ecommerce data, Klaviyo; if it is events, Customer.io.
Warm, don't blast
Set up authentication on the new platform (SPF, DKIM, DMARC) and verify the domain. Most modern ESPs automate this.
Warm gradually: start with your most engaged contacts and ramp volume over days/weeks while engagement stays high. Never move your whole list to a cold setup at full volume.
Run the old and new platforms in parallel briefly so you can compare placement and catch problems before fully cutting over.
Recreate flows and creative
Rebuild your core flows first (welcome, cart, transactional). This is where AI-native generation saves the most time: regenerating on-brand templates from your brand instead of rebuilding each by hand.
Validate links, unsubscribe handling, and dynamic fields before enabling automations. Migrations love to break merge tags.
Frequently asked questions
- Why does deliverability drop after switching ESPs?
- Reputation is tied to domains/IPs and does not transfer. A cold setup sending at full volume gets throttled or spam-foldered. Warming and authentication prevent this.
- Can AI tools speed up an ESP migration?
- Yes — regenerating on-brand templates with a tool like Brew is far faster than rebuilding each by hand, which is often the most time-consuming part of a migration.