Are you looking at switching your email service provider (ESP)? Moving from one ESP to another can be a complex, multilayer process, which also includes evaluating the technical side of your email marketing: i.e. your deliverability configuration. It’s crucial that you do so because switching to another ESP can affect your inbox delivery rate, oftentimes lowering it if your email sending configurations aren’t updated. So, to help you out on this front, our deliverability team has come up 7 deliverability tips to keep in mind while you move from one ESP to another.

#1: Your IP reputation does not transfer over

Inbox providers (ISPs) assess your sender reputation based on a number of variables in their algorithms. Largely, your sender reputation is made up of two components: your IP address reputation and your domain reputation.

With regard to the first aspect, IP address-based reputation, things are a bit tricky. The reason is that when switching to another ESP, your IP address switches as well. This means that the reputation you built on the IP addresses (which can be either shared IP pools or a dedicated IP address) that your prior ESP assigned to you will not be transferred over. The new ESP will use new shared or dedicated IP addresses for your mailings. So, what can you do?

  • If you will be using shared IP addresses, ensure that their reputation is good with a tool such as
  • If you will be assigned dedicated IP addresses, talk to your new ESP about a good ramp-up strategy to warm up the new IPs. To do so, you will likely need to gradually move mailing volume from the old ESP to the new one. Deliverability expert Laura Atkins @ Word To The Wise published some good best practices on this topic.

Unlike the IP address reputation, your domain reputation is very much in your control. But, be careful not to update your IP address AND change your from domain setup at the same time, as this would completely reset your sender reputation, which is a recipe for deliverability disaster.

#2: Check your email authentication

A big part of your sender reputation comes from the email authentication methods (SPF, DKIM, DMARC) you have in place to establish that you are a verified sender. You can check the status of your email authentications from the message headers of your sent emails. For example, in Gmail, you can see this under the Show original option in the drop-down to show the message headers below:

By analyzing the message header, you can see which email authentication protocols are enabled (typically, the format is <protocol name> = pass) and which domains are configured. Here are a few notes on the main three authentication methods:

  • SPF: For the domain used for the envelope sender, which is the one that bounces are sent to and that can be located in the message header under “Return Path.” It’s crucial that you configure your SPF records. Typically the return path address is provided by MailUp, since the system handles your bounces automatically for you, and therefore the SPF record is already configured and there is nothing you need to do. However, in some cases customers wish to personalize the envelope sender: in that case, make sure that the SPF record has been configured for the domain associated with that address.
  • DKIM: In the message header, find the DKIM-Signature that starts with “d=”. Also in this case, if the domain used belongs to your company it helps to use it with your new ESP. All emails sent with MailUp are already, automatically signed with DKIM. Upon request we can configure an optional, client-specific DKIM signature.
  • DMARC: Used mostly as an anti-phishing tool, DMARC was covered extensively in some previous articles on this blog. It’s not commonly adopted by low-volume senders. If it is enabled for your sending domain, however, you should double check that it is configured correctly. An incorrect configuration could cause your emails to not be delivered.

#3: Plan in advance

As a suggestion, plan your move to a new ESP at least one month in advance. The transition should allow for the required steps and account configurations that may take a number of days to complete. As mentioned under #1, if you are moving to new, dedicated IP addresses, they will require some time to be warmed-up, and therefore require that you gradually move your email campaigns from the current to the new ESP. This may translate into additional time needed for the transition, and you should plan for it.

#4: Export your unsubscribe list

Having your unsubscribe list from your old ESP is very important. When switching to your new ESP, you’ll want to import that list so that your mailing lists are up-to-date. If you are moving to MailUp, you can easily import a list of recipients “as unsubscribed”, and also keep unsubscribes synchronized between systems during the transition period by using the MailUp API. View our help guide for more information and use cases.

Also, if you have sign-up forms or apps connected to your ESP, be sure to update those as well.

#5: Keep track of your subscribers

When changing EPS be sure to keep track of the level of engagement of your subscribers. For example, export subscribers from your existing ESP based on their engagement level, and import them into targeted groups in the new ESP (e.g. “Very active subscribers” vs. “Somewhat inactive”). This is important because the move to the new ESP may trigger a loss of email activity data, so that engagement information will be hard to recover if you didn’t record it beforehand. Your new ESP won’t know your subscribers at the start!

#6: Know who handles your company’s DNS records

Know who in your company handles the DNS records for your sending domains, and who can access them. At some point, you’ll have to ask someone in your company (or do it yourself) to update settings in the DNS records, such as adding an SPF record. Managing the DNS records in a timely manner can help you avoid any delays or deliverability issues due to outdated DNS records.

#7: One step at a time. Take your time!

Switching ESPs requires time and you want the transition to be as smooth as possible. So, take it one step at a time!

Even more so if you send millions of email per month as you may experience unexpected delays or limitations.

Start by importing your most engaged subscribers and being your campaigns on the new platform with low sending volumes. This way you will give inbox providers the time to detect the changes in your emailing without raising any red flags such as limiting your inbox volumes or blocking your emails altogether. Again, this should be a gradual process until your sender reputation has been transferred over to the new ESP.

Initially, wait to introduce inactive subscribers (i.e. inactive for more than 3 months) into your new ESP mailing list. This prevents the chance of being too harshly penalized for lower-than-ideal engagement by your recipients while you are still building your “new” sender reputation. It also helps you avoid any chances of emailing to spam traps.

Take extra precautions in the handling of unsubscribed recipients: we’ve seen too many times cases in which they were mistakenly imported as subscribers, only to cause a surge in spam complaints and hard-to-fix sender reputation problems.

Our deliverability team is here to help!

Switching ESPs is not always easy: feel free to comment below with any deliverability questions. Our deliverability team can gladly help!

And, stay tuned for an upcoming e-book on deliverability in partnership with Return Path, the global leader in email intelligence.

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