Migrating to a new email service provider (ESP) is never just a technical change: the process also affects data, design, deliverability and multiple teams.
Lately, more and more companies have migrated to a new ESP. This is happening both because martech platforms are evolving with AI and because some ESPs are disappearing.
For example, one of the first emails I sent was through Mixpanel. (At the time, it wasn’t just focused on analytics and had the ability to send emails.) Then there was Bronto, which Oracle acquired and eventually sunset in 2022. Another platform, Yotpo, deleted Email and SMS functionality in 2025.
Here are 10 practical lessons learned from my experience (and mistakes) during multiple ESP migrations. The goal is to help you prepare for email migration, align with teams, avoid slowdowns, and ultimately improve performance and revenue through migration.
What does an ESP migration actually affect?
Anyone who has ever migrated an ESP knows that the process goes beyond simple export-import and learning new syntax for dynamic customization. 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, operations, etc.).
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These 10 lessons are listed in the order they are usually covered, so you can treat them like a step-by-step checklist.
Lesson 1: Align stakeholders and gain internal support
ESP migration is not just a marketing project; The migration process affects multiple teams and often requires budget, time, and approvals that you should plan in advance.
- Announce the migration internally to all teams concerned.
- Communicate the planned schedule.
- Save time and involvement from development, product, data and other teams.
- Obtain financial approval for the overlap period (see Lesson 2).
- Negotiate a multi-year contract with the new ESP (may include discounts for migration assistance).
Lesson 2: Plan overlap time and team capacity
Migrating to a new ESP does not mean you immediately stop using the old one.
- Expect (and plan for) a period of overlapping costs when paying for both the current and new ESP.
- Talk to the new ESP about a discounted migration period while you configure and don’t yet send your entire email volume.
- Make sure the team understands that they will be working on two different platforms in parallel.
- Consider hiring external help to manage the migration work.
Think of a migration as an opportunity to clean up your email contact lists.
- Define what active or engaged means for your business and delete disengaged contacts.
- Remove hard bounces, invalid emails or spam traps.
- Decide which historical engagement data you actually need (for example, 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 for 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 the time to correctly map attributes and understand data architecture
Teams often map ESP fields quickly and without considering names, types, or future workflows, only to discover broken segments and duplicate attributes.
- Map each 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 types, such as Snake_case or CamelCase) across ESP, CRM, and analytics tools.
- Check the data types (boolean, string, or date) and make sure they match the requirements of the new system.
- Document how subscription preferences are stored and verify how the new ESP handles consent flags and opt-in sources.
- Review synchronization logic to understand how and when data flows between CRM, ESP, and other systems.
Map and save the old attributes that you have not migrated. As with lesson 3, it is recommended to backup and backup all obsolete data and contacts externally.
Lesson 5: Deliverability and infrastructure configuration are essential
Deliverability and infrastructure are often treated as low-priority technical details during an ESP migration, but they can bring the entire migration to a halt if neglected.
- Properly configure 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 tracking engagement and deliverability from day one.
They require dedicated time from IT and other relevant teams, and these integral components should be considered a high priority task.
Lesson 6: Don’t change everything all at once
This may seem like the perfect time to rethink workflows, rewrite copy, and upgrade everything at once. However, each change adds risk and makes troubleshooting much more difficult.
- Separate migration from optimization.
- Copy automations and workflows as they are, instead of rebuilding them on the move.
- Keep the existing copy and design for the first phase.
- Avoid redesigning templates or rewriting message content until the migration is stabilized.
Treat optimization as a separate project once migration is complete.
Lesson 7: Create Reusable Email Marketing Basics
Use the capabilities of the new messaging platform to create a more scalable messaging architecture. Note that this doesn’t contradict lesson 6 (don’t change everything at once), because you won’t be redesigning the appearance.
- Create master templates (e.g. promotional, transactional, and automation emails).
- Create reusable header and footer snippets that can be shared across emails.
- Create modular content blocks (hero sections, CTAs, product grids, etc.) to avoid creating campaigns from scratch.
- Centralize legal and compliance elements to ensure consistency and easy updates everywhere.
Migration is an opportunity to create reusable and scalable foundations using templates, snippets, and modules. This will save time and reduce errors.
Lesson 8: Ensure the quality of your dynamic content and personalization
Dynamic content and personalization can break quietly, resulting in broken variables, empty fields, or incorrect messages for key segments.
- Test all variables used in subject lines, preheaders, body content, and code.
- Check the fallback values for each 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 support platforms and triggers
Because automations and triggers are loosely tied to the legacy email platform or external systems, migrating ESPs often disrupts workflows that people didn’t even know existed.
- Audit potentially hidden automations in marketing, product, sales, and support tools.
- Check the webhooks and API-based triggers and then reconfigure them for the new ESP.
- Validate emails triggered by products and behaviors on the new platform.
Lesson 10: Plan for the next 30 to 60 days
You need a detailed plan for the first one to two months after a completed migration. This plan will allow you to validate the success of the migration.
- Monitor list engagement, spam complaints, bounce patterns, and unsubscribe rates, then periodically compare them to pre-migration baselines.
- Schedule regular check-ins with IT, Product and CRM to validate syncs and workflows.
- Keep your migration notes and playbook up to date with what failed and how you fixed it, just in case you need to perform a future ESP migration.
Start with a clear reason to migrate
An ESP migration is a complex, resource-intensive project that requires time, budget, and alignment across teams. Define your why in concrete terms, like cost savings, new features, improved compliance, or better inbox performance. This will allow you to decide if the move is worth it and measure success afterward.
Ask yourself, “What problem am I trying to solve?” »
- Is this a cost decision?
- Are there any new features I would benefit from?
- Is this a compliance or deliverability solution?
- Is this a provider stability issue?
At the same time, keep an eye on the bigger picture: Inbox AI, stricter privacy rules, and scalable platform capabilities mean ESP migrations will become more frequent rather than rare one-off projects.
Looking back on my own past migrations, the ones that went smoothly were neither the flashiest nor the most advanced. Instead, they were planned well in advance, involved cross-functional collaboration, and received C-level priority and strong support from the new ESP migration team.
Migration is a strategic initiative and not just a technical change
If you remember one thing from this article, let it be this: know the reason why you are changing your email service provider.
Think of it like planting a vineyard: nothing appears overnight. The first months, you juggle between old and new platforms, just as young vines require care before bearing fruit. But once the system matures, you start to reap the benefits: cleaner data, better automations, and a more stable, scalable messaging engine that produces results for years.
