10 lessons from real-world ESP migration

Moving to a new email service provider (ESP) is never just a simple technology change — the process also affects data, design, delivery, and multiple teams.

Recently, many businesses are moving to the new ESP. This is happening both because martech platforms are emerging with AI and because some ESPs are sunsetting.

For example, one of the first emails I ever sent was through Mixpanel. (Back then, it wasn’t just focused on analytics and had the ability to send email.) Then there’s Bronto, which was acquired by Oracle and eventually went into sunset in 2022. Another platform, Yotpo, has removed email functionality and SMS functionality by 2025.

Here are 10 practical lessons from my experiences (and mistakes) in many ESP migrations. The goal is to help you optimize email migration, align teams, avoid downtime, and ultimately improve performance and revenue through migration.

What exactly does ESP migration affect?

Anyone who has ever migrated an ESP knows that the process goes beyond exporting-importing and learning a new syntax for powerful personalization. Affects:

• Data structure (lists, attributes, tags, properties, etc.).
• Design, templates, snippets, and blocks.
• Transactions, automation, and lifecycle flows.
• Delivery, domain, and IP reputation.
• Multiple teams within your organization (sales, IT, sales, support, legal, ops, etc.).

These 10 lessons are organized in the order they are most often studied, so you can think of 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 involves many parties and often requires budget, time, and permits that you need to plan in advance.

• Announce the move internally to all relevant groups.
• Communicate the expected timeline.
• Secure time and engagement from dev, product, data, and other teams.
• Get financial approval during the overlap period (see Lesson 2).
• Negotiate a multi-year contract with the new ESP (may include discounts to support migration).

Lesson 2: Schedule time to overlap with group dynamics

Moving to a new ESP does not mean you immediately stop using the old one.

• Expect (and budget for) a period of excess expenses as you pay for both the current ESP and the new one.
• Talk to a new ESP about a discounted migration period while you’re setting up and haven’t sent your full email volume.
• Make sure the team understands that they will be working on two different platforms in parallel.
• Consider bringing in outside help to handle the relocation process.

Treat migration as an opportunity to clean up your email contact list.

• Define what it means to be active or engaging in your business and remove contacts who are not engaging.
• Suppress hard bounces, invalid emails, or spam traps.
• Determine what contact history data you really need (eg, the last 12-24 months), saving the entire cache instead of importing it.

Keeping offline contacts and old interaction data can cost you in storage costs in your ESP. Cleaning up your inventory and historical data can save you budget, and you can export the data and store it externally.

Lesson 4: Take the time to properly map attributes and understand data structure

Teams often map ESP fields quickly and without considering naming conventions, types, or future workflows, only to later find broken segments and duplicate attributes.

• Map every field from the old ESP to the new ESP, and define which fields actually need to be migrated (and which can be migrated).
• Standardize naming conventions (and case type, such as snake_case or camel) across ESP, CRM, and analytics tools.
• Check the data types (boolean, string, or date) and ensure they match the requirements of the new system.
• Document how subscription preferences are stored, and verify how the new ESP handles permission flags and login sources.
• Explore synchronization logic to understand how and when data flows between CRM, ESP, and other systems.

Map and save old attributes that you haven’t migrated. As with Lesson 3, it is recommended to back up and save all outdated data and contacts externally.

Lesson 5: Delivery and setting up of infrastructure is critical

Delivery and infrastructure are often considered the least important technical details during an ESP migration, but they can derail the entire migration if neglected.

• Properly setup and verify SPF, DKIM, and DMARC authentication for the new ESP before deploying to scale.
• Decide whether you need a dedicated IP or a shared IP based on your volume.
• Set up a slow IP or domain warming strategy.
• Start engaging and monitoring delivery from day one.

They need time dedicated to IT and other key groups, and these key components should be prioritized as the most important task.

Lesson 6: Don’t change everything at once

It may seem like the perfect time to redesign the workflow, rewrite the copy, and improve everything all at once. However, every change adds risk and makes troubleshooting more difficult.

• Separate migration from development.
• Copy automations and workflows as they are, instead of rebuilding them during the move.
• Keep a copy of the existing and the first stage design.
• Avoid redesigning templates or rewriting message content until the migration is stable.

Manage the configuration as a separate project after the migration is complete.

Lesson 7: Build reusable email marketing basics

Use the capabilities of the new email platform to create even more sophisticated email designs. Note that this does not contradict Lesson 6 (don’t change everything at once), as you won’t be redesigning the look and feel.

• Create primary templates (eg, promotional, transactional, and automated emails).
• Create a header and footer that can be shared across all emails.
• Create modular content blocks (hero sections, CTAs, product grids, etc.) to avoid building campaigns from scratch.
• Include legal and compliance aspects to ensure consistency and facilitate review across the board.

Migration is an opportunity to build reusable, scalable infrastructure using templates, snippets, and modules. Doing so will save time and reduce errors.

Lesson 8: Test your dynamic content and personalization

Dynamic content and personalization can silently break, resulting in broken variables, empty fields, or incorrect messages for key segments.

• Check all types used in subject lines, pre-headers, body content, and code.
• Check the return values ​​of every key field.
• Validate conditional logic (if/if conditions, show/hide blocks).
• Review localization considerations, including language translations, currency, and regional formatting.

Lesson 9: Explore and connect supporting platforms and triggers

Because automations and triggers are loosely tied to legacy email platforms or external systems, migrating ESPs often break workflows people didn’t even know existed.

• Explore potential automations hidden in marketing, products, sales, and support tools.
• Test API-based webhooks and triggers, and reconfigure them in the new ESP.
• Validate product-driven emails and behaviors in the new environment.

Lesson 10: Plan the next 30-60 days

You need a detailed plan for the first to two months after the migration is completed. This plan is how you will ensure the success of the migration.

• Monitor engagement, spam complaints, bounce patterns, and churn lists, and periodically compare to pre-migration benchmarks.
• Schedule regular check-ins with IT, product, and CRM to ensure sync and workflow.
• Keep your migration notes and playbook updated on what broke and how to fix it — in case you need to migrate to ESP in the future.

Start with a clear reason for moving

An ESP migration is a complex, resource-intensive task that requires time, budget, and team alignment. Describe your reason in concrete terms, such as cost savings, new capabilities, improved compliance, or better inbox performance. This will allow you to decide if the move is worth the effort and measure success afterwards.

Ask yourself, “What problem am I trying to solve?”

• Is it a cost decision?
• Are there new skills I could benefit from?
• Is it a compliance or delivery solution?
• Are you concerned about the stability of the seller?

At the same time, keep an eye on the big picture: Inbox AI, strict privacy laws, and evolving platform capabilities mean that ESP migration will become more common than rare jobs.

Looking back on my past migrations, the ones that went well weren’t the first ones or the most advanced ones. Instead, they were organized in advance, involved a variety of interactions, and received C-level prioritization and strong support from the new ESP migration team.

Migration is a strategic plan and not just a technological change

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 happens overnight. In the first few months, you are going through the old and new fields, as the young vines need to be cared for before they bear fruit. But as the system matures, you begin to enjoy the benefits: cleaner data, better automations, and a stable, sharp email engine that produces results for years.