Good news: your company's email list had a recent growth spurt. You're sending more email than ever—to a larger audience—and with all that growth it's time to consider a new email service provider (ESP).

CMOs and CTOs looking to upgrade ESPs too often meet with frustration, however, because migration to a new platform can be tricky—and it can have a deeply positive or negative impact on a company's sender reputation and, ultimately, on customer communications.

Because email is a major channel that companies rely on for generating revenue, mistakes can have a lasting impact on your bottom line.

To safely navigate your migration, we've compiled a list of five common blunders. By avoiding these five mistakes, marketers and tech teams will save hours of work and ensure a positive outcome.

Mistake 1: Switching Service Providers Before Optimizing Your Email List

Frustration often compels many companies to switch providers because their emails aren't landing in their customers' inboxes. Though a new platform can help with deliverability issues, landing in a user's spam box is often the result of a list stuffed with ancient email addresses and low engagement and high bounce rates.

Before you invest in a migration, ensure you've optimized your list by cleaning it thoroughly, removing bouncing addresses and reconfirming with your current contacts that they are still interested in receiving your messages.

Mistake 2: Not Scaling Your Staff Along With Your Platform

The bigger your list, the more complex a strategy needed to get the most from it, so it's important to hire an expert who can steer the ship to a more sophisticated platform after the migration.

To develop an expert email strategy, you need a professional to help with...

  • Boosting your open and click rates. An expert can identify the best time and circumstance to send your emails.
  • Ensuring your newsletter is optimized—subject line, html design, copywriting, and landing pages. An expert will be able to run experiments, leading to better overall engagement.
  • Sprucing up an old email list by removing inactive recipients, and dividing the list into more complicated segments such as by gender. Better lists equal better deliverability.

Mistake 3: Undoing a Good Sender Reputation

As an email sender, your reputation is paramount. You can damage it two ways during a migration:

  1. Failing to migrate data
  2. Sending too many emails too soon.

Failing to Migrate Data

The integrity of an email list impacts deliverability rate. Part of building a quality list is updating it after each send. When a company leaves an old email service provider, it risks losing the valuable data it collected to improve list quality—bounces, unsubscribes, and spam complaints, for example.

To carry your established reputation to the new platform, you must be careful not to close your account with your existing email provider until you know 100% that you have transferred the essential information. Many email providers offer tools that analyze the quality of the email list so you can ensure your contacts have successfully migrated.

Sending Too Many Emails Too Soon

When companies launch their first email campaign, they typically use a shared IP address so that it's affordable. With a shared IP, however, your reputation can be affected for better or worse by other accounts using the same IP address.

When you're ready to migrate to a new platform, you're also likely ready for a dedicated IP address, which means your company is itself entirely responsible for your sender reputation. Starting with a fresh, dedicated IP address requires investment.

Before resuming your regular email schedule, or implementing a new one, you need to first build the reputation of your new IP address by gradually raising the amount of email sent every day.

If your domain name has a good reputation and you have a clean contact list—no more than a 3% bounce rate—your reputation should be restored and should begin improving within 7-40 days.

Mistake 4: Failing to Authenticate Sender Identity

Simple Mail Transfer Protocol (SMTP) is an Internet standard for email transmission. On its own, though, SMTP doesn't provide a built-in mechanism to verify a sender's identity. So, theoretically, anyone can send a message using, say, the email address That presents a huge problem for brands, financial institutions, and politicians!

To avoid that problem, email specialists developed two authentication methods to protect and verify sender identity: Sender Policy Framework (SPF) and Domain Keys Identified Mail (DKIM). If those two methods are not established during migration, it's likely the ISPs will reject your email or relegate it to the spam folder.

  • Sender Policy Framework builds a bridge between your sending IP address and domain name. With SPF, an ISP can, for example, verify that PayPal (rather than a scammer) owns the server that sends you an email.
  • Domain Keys Identified Mail allows the ISP to ensure that no one can change the content of an email while it's in transit.

Mistake 5: Assuming the Migration Is Finished

Don't undo the work of a successful migration by getting too comfortable. The email game is always evolving, and you are never protected against future deliverability issues.

Be sure to track CAN-SPAM law and ISP regulation changes to ensure continued compliance.

Most important: listen to your customers. Review past campaign performance against current campaigns and monitor changes in recipient behavior.


If email migration is completed successfully, the investment to move to a new ESP will be worth it. Post-migration open rates should be higher due to improved deliverability, and clickthrough rates should improve because recipients are more engaged with your content. Also, keep an eye on your bounce rate to confirm you're not experiencing a throttling issue with any ISPs.

Ultimately, successful campaigns look different from each other, depending on the sender's industry and business goals, but working on those metrics will get you off to a good start and ensure that you won't have to spend time on another ESP migration in the near future.

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Five Deadly Email Platform Migration Mistakes to Avoid

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image of Anthony Marnell

Anthony Marnell is the North American VP of Mailjet, an all-in-one email service provider with over 25,000 customers worldwide.

LinkedIn: Anthony Marnell

Twitter: @AnthonyMarnell