Email Infrastructure and Service Providers

How to Survive Your Next ESP Migration—Without Damaging Email Performance

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It’s all very exciting: Your company has outgrown its email marketing platform, and it’s on to bigger and better things. You’ve been told the new email service provider (ESP) has all the bells and whistles, and integrates right into your powerful CRM.  

Moving day is coming soon, so it’s time to prepare.

How hard could it be?  

Unfortunately, migrating ESPs is one of the biggest risks an email marketing program can face. Fail to manage this project correctly, and you could end up with a big mess from an email performance and revenue standpoint. 

With solid organization, time management, and the right resources, email marketers can ace their next migration.  

Let’s take a look at some of the potential consequences of a poorly managed ESP migration and how to prevent these issues. 


Your sender reputation relies on subscribers and mailbox providers trusting that your messages are legitimate. When you move to a new service, your email will be sent from a new infrastructure that has no verifiable sending history. If there’s no evidence that it has permission to send on your company’s behalf, you could run into low inbox placement and IP blocks because email providers will assume you are a spammer attempting to impersonate your company.

Domain Name System (DNS) records need to be updated at least twice during this project. While you are still using your old ESP but before you begin sending from your new ESP, you’ll want to confirm which DNS records (MX, SPF, DKIM, and CNAME) you need to add or update with your new ESP. This will require coordination with your DNS Administrator and Change Management. Once your old ESP’s account is no longer active, update or delete the DNS records that validated the old service as an approved sender.  

Content and triggered campaigns

To maintain brand consistency, migrate your email templates, images, landing pages, and any other web content to the new system. You’ll need to update relevant links (e.g., unsubscribe links) in your email templates to ensure that subscription preferences get recorded in your new ESP. It’s also critical to plan for a smooth transition for automated email series.  

You don’t want participants to get cut off mid-journey during this transition period. Reconstruct automations in the new ESP, ensuring that past participants are not accidentally re-started at the beginning again.  

Subscription management

Keeping track of your subscribers’ preferences can be tricky during the migration process. First, clean your marketing lists in your old ESP, removing anyone who has been suppressed due to blocks, complaints, hard bounces, inactivity, or unsubscribes. A contact verification tool like Validity BriteVerify will make this process easier and less prone to human error. 

Then, create your subscription management center/email preference center and link to it in your email templates in your new ESP. Next, import your subscription-based marketing lists. Finally, link to your new subscription center in all marketing templates. If you continue to use your old ESP during the migration process, you will need to keep track of any new bounces, blocks, complaints, or unsubscribes to update lists in your new ESP.  

Data issues

This is the big one. It’s important to coordinate this project with all relevant teams, establish hard (but realistic) deadlines, and allow for any overlapping time before your old ESP contract expires. Otherwise, you could end up with invalid, outdated, or missing data in your database. This will lead to hard bounces, spam complaints, and spam trap hits. Right out of the gate, you could end up with a damaged sender reputation. To prepare your data for the big move, take these steps:   

  • Clean your database: Merge duplicates. Delete invalid addresses from your database. Remove unsubscribed addresses from subscription-based marketing lists. Make sure these contacts are marked as opted out/unsubscribed so they will be suppressed in the new ESP. Consider archiving contacts who have not engaged (clicks, purchases, submitted forms, etc.) in a defined period of time.
  • Configure Lead/Contact forms with custom fields that match those used in your old database to make importing easier. 
  • Export your clean contact data, reports, and images from your old ESP, making sure to keep backup copies. 
  • Import data into the new ESP/CRM, matching all relevant fields on your records. 

IP warming

Migrating to a new ESP requires you to send from new IP addresses. Shared IP addresses do not require warming, but with dedicated IP addresses, you’ll need to slowly ramp up your sending volume. (MBPs view sudden activity from a new IP as spamlike behavior and will filter messages accordingly.)    

Depending on your average sending volume and cadence, the warming process can take several weeks. Test the waters before sending to your full audience to identify any deliverability issues by performing inbox placement tests. When segmenting your marketing audiences during the IP warm-up process, send to highest engaged subscribers first. Expand to the less engaged audience cautiously, adjusting strategy if you encounter high bounce rates or IP blocks. If you continue to use the old ESP during warm-up, make sure that any additional unsubscribed or bounced contacts are updated in the new ESP.  Once you’ve completed your successful warm-up, you may start sending to your contacts at your normal volume and frequency. After confirming that everything is running smoothly, you may finally fully transition all emails to your new ESP.   


A smooth ESP migration requires an enormous, coordinated effort, but the payoff will be worth it. You may even see better deliverability than you did from your old ESP now that you are starting with a freshly cleaned database and improved processes.  

For an in-depth look at how leading retailer J.Jill switched their ESP three times in three years, read our case study: “J.Jill maintains a consistent ~100% inbox placement rate throughout three ESP migrations with Validity Everest.”



Validity customers:  Need additional consulting? Reach out to your customer success manager to coordinate with Validity Professional Services.