Start with the app you are leaving, not the app you want to try. Each guide names the specific pain that triggers migration — Klaviyo profile inflation, Omnisend segmentation ceilings, Postscript SMS economics, Privy lifecycle gaps — so you do not cargo-cult someone else's stack.
Run the migration checklist on that page before signing annual contracts. Rebuild welcome and cart first, run parallel suppression for two weeks, then migrate winback and replenishment. Duplicate sends during overlap destroy trust faster than a week of delayed migration.
Sequenzy ranks first on most pages when the bottleneck is decision fatigue and pay-per-email economics, not raw predictive maximums. Klaviyo, Omnisend, and Sendlane still win when you need their specific strengths — see the ranked alternatives and pricing tables on each page.
Full app rankings → · Sequenzy vs Klaviyo → · Store-type guides →
Integration dependency audit before any incumbent platform disconnect
Platform exits fail operationally when connected apps keep pushing data into a system you partially deactivated. Before disconnecting any incumbent platform from Shopify, inventory every integration: subscription tools, loyalty apps, review platforms, helpdesk systems, popup capture tools, and SMS coordination partners. For each integration document data direction, events triggered, segments or tags modified, and business criticality. Critical integrations must reconnect on the replacement platform before core automations go live. Low-value integrations from deprecated apps should sunset rather than migrate — most merchants accumulate integration debt that amplifies migration risk beyond the core Shopify email migration transition itself.
Capture tools feeding any incumbent platform list IDs require theme and checkout audit. Grep storefront theme files, checkout extensions, and post-purchase pages for hardcoded list identifiers or webhook URLs pointing at any incumbent platform. SMS coordination with email recovery needs documented suppression owner per trigger type — email platform and SMS platform optimizing independently creates customer complaints within days of overlap. Export UTM and campaign naming conventions if analytics dashboards depend on any incumbent platform campaign structure; attribution reporting resets during migration quarter unless naming discipline transfers deliberately.
Quarterly optimization after leaving any incumbent platform
First thirty days post-migration focus on suppression integrity and deliverability stability. Days thirty through ninety focus on revenue optimization by flow type. Archive any incumbent platform baseline metrics during migration — attributed revenue by automation, send volume, complaint rate, recovery timing — and compare weekly against new platform performance. Cart recovery should reach parity within two weeks; winback and replenishment should exceed old platform performance if migration rationale was capability upgrade rather than pure cost reduction. Underperformance triggers suppression audit before creative audit — overly aggressive recent-buyer exclusions silently prevent enrollment more often than weak subject lines.
Segment hygiene at day sixty prevents repeating billing or deliverability problems under new platform model. Sunset unengaged contacts regardless of how new platform bills — per-contact, per-send, or flat tier. Quarterly review documents which automations required manual intervention versus ran untouched; increasing untouched percentage indicates playbook stabilization. Deliverability seed tests at day thirty and ninety on Gmail and Outlook catch reputation issues before they compound across peak promotional calendar.
Building the business case and choosing replacement timing
Finance approves migration with conservative revenue projections, not feature checklists. Present twelve-month cost of staying on any incumbent platform including platform fees, operator labor, agency support, and opportunity cost of flows the current platform cannot run. Present migration cost: labor, agency rebuild, deliverability ramp risk, and three-month conservative incremental revenue projection from flows enabled on replacement platform. Break-even month calculation determines urgency — fee-only savings with twelve-month payback rarely justify migration; revenue lift with four-month payback usually does. Negotiate with any incumbent platform once before migrating if contract renewal is near; documented competitive quotes sometimes reduce renewal cost enough to fund hybrid improvement without full exit.
Replacement timing should avoid peak revenue weeks — post-BFCM January, post-Valentine March lull, mid-summer for seasonal categories. Never port SMS numbers during highest promotional month. Never run parallel cart recovery through busy sale weekend without named kill-switch owner available in real time. Migration is operational project with revenue risk; schedule it deliberately rather than reacting to invoice frustration with rushed cutover that costs more in duplicate sends and deliverability damage than platform fees ever did.