10 lessons from real-world ESP migrations

Migrating to a new email service provider (ESP) is never just a simple technical switch — the process also touches data, design, deliverability, and multiple teams.Lately, more and more businesses have been migrating to a new ESP. This is happening both because martech platforms are evolving with AI and because some ESPs are being sunset. For example, one of the first emails I ever sent was through Mixpanel. (Back then, it wasn’t solely focused on analytics and had the capability to send email.) Then there was Bronto, which Oracle acquired and eventually sunset in 2022. Another platform, Yotpo, removed email and SMS functionality in 2025. Here are 10 practical lessons from my experience (and mistakes) across multiple ESP migrations. The goal is to help you prepare for email migration, align with teams, avoid slowdowns, and eventually improve performance and revenue through the migration. What does an ESP migration really touch? Anyone who has ever migrated an ESP knows that the process goes beyond just export‑import and learning new syntax for dynamic personalization. It affects: Data architecture (lists, attributes, tags, properties, etc.). Design, templates, snippets, and blocks. Transactional, automated, and lifecycle flows. Deliverability, domain, and IP reputation. Multiple teams within your organization (marketing, IT, sales, support, legal, ops, etc.). Your customers search everywhere. Make sure your brand shows up. The SEO toolkit you know, plus the AI visibility data you need. Start Free Trial Get started with These 10 lessons are arranged in the order they are usually addressed, so you can treat them as a step‑by‑step checklist. Lesson 1: Align stakeholders and secure internal support Migrating ESPs is not just a marketing project; the migration process affects multiple teams and often requires budget, time, and approvals that you need to plan for in advance. Announce the migration internally to all relevant teams. Communicate the expected timeline. Secure time and involvement from the dev, product, data, and other teams. Get financial approval for the overlap period (see Lesson 2). Negotiate a multi‑year contract with the new ESP (can include migration‑support discounts). Lesson 2: Plan for overlap time and team capacity Migrating to a new ESP doesn’t mean you immediately stop using the old one. Expect (and budget for) a period of overlapping costs as you pay for both the current ESP and the new one. Talk to the new ESP about a discounted migration period while you’re setting up and not yet sending your full email volume. Ensure the team understands they’ll be working on two different platforms in parallel. Consider bringing in external help to handle migration work. Lesson 3: Audit, clean, and validate your email contact lists Treat a migration as an opportunity to clean up your email contact lists. Define what active or engaged means for your business and remove disengaged contacts. Suppress hard bounces, invalid emails, or spam traps. Decide what historical engagement data you really need (e.g., the last 12-24 months), archiving the rest rather than importing it. Maintaining disengaged contacts and old engagement data can cost you in storage fees from your ESP. Cleaning up your lists and historical data can save you budget, and you can always export the data and store it externally. Lesson 4: Take time to properly map attributes and understand data architecture Teams often map ESP fields quickly and without considering naming, types, or future workflows, only to later discover broken segments and duplicated attributes. Map every field from the old ESP to the new ESP, and define which fields actually need to be migrated (and which don’t). Standardize naming conventions (and case type, such as snake_case or camelCase) across the ESP, CRM, and analytics tools. Check data types (boolean, string, or date) and ensure they match the new system’s requirements. Document how subscription preferences are stored, and verify how the new ESP handles consent flags and opt‑in sources. Check the sync logic to understand how and when data flows between the CRM, ESP, and other systems. Map and save old attributes you didn’t migrate. As with Lesson 3, it’s recommended to back up and save all outdated data and contacts externally. Lesson 5: Deliverability and infrastructure setup are critical Deliverability and infrastructure are often treated as low‑priority technical details during an ESP migration, but they can break the entire migration if overlooked. Correctly set up and validate SPF, DKIM, and DMARC authentication for the new ESP before sending at scale. Decide whether you need a dedicated IP or a shared IP based on your volume. Plan a gradual IP or domain warm‑up strategy. Start engagement and deliverability monitoring from day one. They require dedicated time from IT and other relevant teams, and these integral components should be prioritized as a high‑priority task. Lesson 6: Don’t change everything at once It might seem like the perfect moment to redesign workflows, rewrite copy, and upgrade everything at once. However, every change adds risk and makes troubleshooting much harder. Separate migration from optimization. Copy automations and workflows as they are, instead of rebuilding them during the move. Keep the existing copy and design for the first phase. Avoid redesigning templates or rewriting message content until after migration stabilizes. Treat optimization as a separate project after the migration completes. Lesson 7: Build reusable email marketing foundations Use the new email platform’s capabilities to build a more scalable email architecture. Note that this doesn’t contradict Lesson 6 (don’t change everything at once), as you won’t be redesigning the look and feel. Create master templates (e.g., promotional, transactional, and automation emails). Build reusable header and footer snippets that can be shared across all emails. Create modular content blocks (hero sections, CTAs, product grids, etc.) to avoid building campaigns from scratch. Centralize legal and compliance elements to ensure consistency and ease updates everywhere. Migration is an opportunity to build reusable, scalable foundations using templates, snippets, and modules. Doing so will save time and reduce errors. Lesson 8: QA your dynamic content and personalization Dynamic content and personalization can quietly break, causing broken variables, empty fields, or incorrect messaging for key segments. Test all variables used in subject lines, preheaders, body content, and code. Check fallback values for every key field. Validate conditional logic (if/else conditions, show/hide blocks). Review localization logic, including language versions, currency, and regional formatting. Lesson 9: Audit and connect supporting platforms and triggers Because automations and triggers are loosely tied to the old email platform or external systems, migrating ESPs often breaks workflows people didn’t even know existed. Audit potentially hidden automations in marketing, product, sales, and support tools. Check webhooks and API‑based triggers, and reconfigure them for the new ESP. Validate product‑ and behavior‑triggered emails on the new platform. Lesson 10: Plan for the 30-60 days that follow You need a detailed plan for the initial one to two months following a completed migration. This plan is how you’ll validate the migration’s success. Monitor engagement, spam complaints, bounce patterns, and list churn, then periodically compare them to pre‑migration benchmarks. Schedule regular check‑ins with IT, product, and CRM to validate syncs and workflows. Keep your migration notes and playbook updated with what broke and how you fixed it — just in case you need to conduct a future ESP migration. Start with a clear reason for migrating An ESP migration is a complex, resource‑heavy project that demands time, budget, and cross‑team alignment. Define your why in concrete terms, such as cost savings, new capabilities, improved compliance, or better inbox performance. This will allow you to decide whether the move is worth the effort and measure success afterward. Ask yourself, “What problem am I trying to solve?” Is it a cost decision? Are there new capabilities I would benefit from? Is it a compliance or deliverability solution? Is it a vendor stability concern? At the same time, keep an eye on the bigger picture: Inbox AI, stricter privacy rules, and evolving platform capabilities mean that ESP migrations will become more frequent rather than rare one‑off projects. Looking back at my own past migrations, the ones that went smoothly weren’t the flashiest or most advanced. Instead, they were planned well in advance, involved cross‑functional collaboration, and received C‑level prioritization and strong backing from the new ESP’s migration team. Migration is a strategic initiative and not just a technical switch If you remember one thing from this article, let it be this: Know your reason for moving email service providers. Think of it like planting a vineyard — nothing shows up overnight. For the first couple of months, you’re juggling old and new platforms, just as young vines demand care before they bear fruit. But once the system matures, you start enjoying the benefits: cleaner data, better automations, and a more stable, scalable email engine that produces results for years. The post 10 lessons from real-world ESP migrations appeared first on MarTech.