How do you migrate from one ESP to another safely?

ESP migration requires careful planning to avoid deliverability disruption. Rushing causes problems; methodical transition protects your reputation.

• Pre-migration:
• Audit current setup: authentication records, sending domains, tracking domains, suppression lists
• Document everything: templates, automations, integrations, API usage
• Export suppression lists: bounces, unsubscribes, complaints (critical)
• Parallel running phase:
• Set up new ESP completely before switching traffic
• Verify authentication (SPF, DKIM, DMARC) works correctly
• Test thoroughly with seed lists
• Keep old ESP active as backup
• Traffic migration:
• Start with small percentage of traffic to new ESP
• Monitor deliverability closely
• Gradually increase new ESP traffic over weeks
• Warm new IPs if dedicated
• Don't rush; respond to signals
• DNS transition:
• Update SPF to include both ESPs during transition
• Add new DKIM records before sending from new ESP
• Only remove old ESP from records after full migration
• Post-migration:
• Verify all automations work correctly
• Confirm tracking and reporting function
• Keep old ESP accessible for historical data
• Update documentation
• Change ships in calm waters, not during a storm. Plan migrations during low-volume periods when possible.