ESP Migration Cost Calculator

Where migration cost actually accumulates

The calculator's number captures the work directly tied to migration. The harder cost to estimate is the deliverability dip during the cutover — the period when reputation on the new infrastructure is still building while reputation on the old infrastructure is being abandoned.

For most migrations that window is 4-8 weeks. During it, placement at major mailbox providers can drop 10-20 points before recovering.

Three components carry most of the cost. Template rebuilding is the largest line item for visually-rich programmes; transactional senders with simple text emails migrate in hours, e-commerce senders with dozens of dynamic templates take weeks. Automation flow recreation is the second-largest cost, particularly when migrating from Klaviyo or HubSpot where flow logic depends on platform-specific data structures that do not export cleanly. IP warming on dedicated infrastructure takes 4-6 weeks regardless of how fast the technical migration runs — this is the schedule constraint, not the team's velocity.

What separates the three migration types

The "ESP to ESP" path migrates between two managed services. Templates, automations, and lists all need rebuilding because no two ESPs structure these primitives the same way. The schedule is dominated by team capacity rather than infrastructure constraints; warming is faster because the new ESP has warm shared IPs available.

The "ESP to dedicated infrastructure" path adds IP warming as a binding constraint. The technical work compresses to 2-4 weeks; warming extends total elapsed time to 6-10 weeks. This is the migration that produces the largest long-term cost reduction (60-80% off Klaviyo-class pricing at scale) but has the longest fragile-state window.

The "self-managed to managed" path is the cheapest and fastest because the underlying infrastructure does not change — only the operational responsibility moves. This is usually a 2-4 week migration with minimal deliverability risk.

Migration mistakes the calculator does not model

• Migrating during peak revenue periods. Black Friday e-commerce migrations are the canonical example. The deliverability dip during a high-revenue window costs more than the migration saves; schedule major migrations for low-revenue periods (January-February, August-September).
• Skipping the re-permission step. Importing a list to a new ESP without re-confirming consent is technically a GDPR violation in EU jurisdictions, and produces the complaint-rate spike that derails the warming phase. The right pattern: re-permission campaign at the old ESP, then migrate confirmed subscribers only.
• Running two ESPs in parallel for "safety." Operationally appealing, deliverability disaster. Both domains share the same From: address with conflicting authentication, which produces DMARC alignment failures and unpredictable placement.
• Not retaining the old ESP's reputation through the cutover. Cancelling the old ESP on day 1 of the new infrastructure abandons the reputation that took years to build. Keep the old ESP active in parallel for the first 30-45 days, draining volume gradually to the new infrastructure as it warms.