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ESP Migration Guide for SaaS and Product-Based Companies

Scaling issues, poor deliverability, rising costs, missing features, slow support — there are just a few reasons to switch your email service provider. If your current ESP makes you jump the hook every time you need to scale your sending or keep emails out of spam folders, this step-by-step guide will help you plan and execute your migration smoothly.

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ESP migration: a checklist

Before we dive into technical and not only details, here’s a quick checklist you can use to plan your ESP migration:

Audit your current ESP setup:

Prepare your data for migration

Set up your technical infrastructure at the new ESP

Configure access controls and security

Set up integrations and webhooks

Test in staging, then check deliverability and inbox placement

Plan the timing and phasing of the migration

Monitor post-migration performance

ESP migration cheat sheet

Now, let’s see how to change your email service provider step-by-step.

Step 1. Audit the current ESP setup

Yes, ESP migration is a big deal, yet with a clear plan, you can change the provider without breaking operation, data losses, and deliverability drops. 

By this point, I assume you’ve already done your homework and know exactly which ESP you want to migrate to. If not, it’s worth checking our guide on how to choose the email sending provider for your specific business needs, or check these articles:

Already know your hero? It’s time to analyze how your current setup works. The goal is to document what’s in place today, so you can plan the migration with fewer risks and no missed steps.

Look at:

The gathered information will help you understand what will move, what might need reconfiguring, and what you’ll need to test after the migration.

Step 2. Export current data

After the audit, export the data you’ll need for the migration to make sure no valuable information gets lost during the switch.

Here’s what you need to export:

Additionally, you can also save:

Step 3. Set up your technical infrastructure and warm up your domain

Now that you have your data ready, it’s time to configure the technical aspects of your new ESP. 

If you’re migrating at a large scale, you can request migration support from your new email service provider to streamline the process and be sure all your specific requests and needs are taken into account. Mailtrap, for example, offers dedicated support for large-scale senders, helping you with the transition and smooth infrastructure setup.

With or without external help, focus on these key tasks:

Step 4. Configure 2FA and user access controls

Before you start sending emails, make sure your account is secure. Enable two-factor authentication for all users. This adds an extra layer of protection by requiring both a password and a secondary form of verification to log in.

Next, review permission levels within your new ESP. Many platforms support fine-grained roles that let you control access to key areas, like sending settings, contact lists, analytics, or billing. Assign roles based on team responsibilities to streamline workflows and reduce the risk of errors or data exposure.

Finally, set up activity logs to track user actions within the platform. These logs help you monitor who’s making changes, accessing sensitive information, or updating configurations. The feature helps you detect issues early or prove compliance with data regulations like GDPR, APA, CCPA, and others.

Step 5. Upload your data and setup integrations

Take the contact lists, templates, and other important data you exported earlier and upload them into your new ESP. In some cases, your email templates may not import directly, and you might need to rebuild them using the new ESP’s tools.


Connect your tools and platforms, such as CRMs, marketing automation systems, or eCommerce platforms, to your new ESP. This helps keep your workflows running smoothly once you begin sending live emails. ​​For smooth operations, you need to set up:

If your new ESP uses webhooks for engagement tracking, set up and validate those endpoints early on. Webhooks are often used to push real-time events like bounces, unsubscribes, opens, or clicks to your system. Make sure your receiving endpoint is authenticated, can parse payloads correctly, and handles retries or malformed data. Run test events (if the ESP allows it) or simulate webhook calls locally to confirm that data is being received and processed as expected. This will help avoid missed events or broken reporting once you go live.

Step 6. Test the setting, email deliverability, and inbox placement

Start by simulating your real sending environment, run test calls through your API, trigger automated workflows, and validate integration points with your CRMs, databases, or backend logic. Focus on confirming that the right templates are pulled, variables are populated, and emails are successfully handed off to the ESP. If you use SMTP, double-check authentication and error handling. If you rely on an API, verify response codes, retry logic, and payload structures.

You can run these tests in a controlled environment using tools like Mailtrap Email Sandbox. It allows your dev team to confirm that sending logic works as expected, without worrying about inbox delivery or user-facing content just yet.

Once your system behaves as expected, move to testing email deliverability and inbox placement. Start with a small batch of live sends to different mailbox providers. Check how your emails render in real inboxes, verify that tracking links work, images load properly, and unsubscribe links are functional.

You can also use Mailtrap Email Sandbox for it. ​​Sandbox functions as a fake SMTP server and allows you to inspect full email content and headers without sending anything to real recipients. 

Then, use inbox placement tools to analyze where your emails land, inbox, spam, or promotions. This gives you early visibility into potential filtering issues and helps fine-tune your domain or IP warm-up process.

Step 7. Schedule the final transition

This step will help you check there’s minimal disruption to your ongoing operations. Here’s what to begin with:

Step 8. Monitor post-migration performance

Once your migration is complete and you’re live with your new ESP, you need to regularly monitor key metrics to make sure everything is functioning as expected. Keep a close eye on:

Set up automated alerts or dashboards to monitor spikes in errors, bounce rates, or delivery delays. The first few days after migration can show some changes, but you need to monitor for at least a couple of weeks to get a true sense of how things are settling.

Watch out for bounce rates and unsubscribes after migration, too. If these numbers start to go up, it could signal deliverability issues with your new ESP. Spotting and fixing them early helps support your critical business communications.

Wrapping up 

If you’re not seeing the growth you need because your current provider can’t handle your increasing email volume or you’re facing constant issues with inbox placement, it’s time for a change. With the right planning and tools, you can switch providers smoothly, without major workflow interruptions or declining email delivery rates.

Considering Mailtrap as your next ESP? These detailed step-by-step migration guides for popular providers will be very helpful:

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