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Why Email Duplicates Matter

This blog post originally appeared on the Marketo blog, written by Katja Keesom, an active member of the Marketo community as well as a Chapman Bright Senior Consultant. 

The health of your database is of great importance to the effectiveness of your Marketing Automation. So why exactly should you be concerned about email duplicates? Well, there’s a number of reasons.


  1. Personalization

Let’s say John and Chris both work for Example Inc. and in both their profiles the email address listed is For your next campaign, John qualifies and is sent an email. With the same email address for both men, you have no control over who reads the email, so you might not be addressing the person reading the email.

  1. Activity history

Following from that scenario, if Chris opens that email instead of John and clicks on a link, Marketo does not attribute those activities to Chris, but to John instead as his mkto-token is associated with the email. Better yet, if Chris had accepted a cookie, that cookie is now also associated with John. That means subsequent web visits by Chris will be attributed to John. You can imagine how this will become quite a mess over time as multiple interactions take place and cookies swap back and forth.

  1. Lead processes

Again, following through this scenario, John will be accumulating points in your lead scoring model, whilst the real activity is by Chris. It is entirely imanginable that this will hit the lead scoring threshold and John will be sent to Sales for follow up. That will be quite the surreal conversation, as John knows nothing about all these interactions. So duplicates will mean your lead scoring process becomes ineffective.

  1. List uploads

If you have included an email address in a csv file to upload into Marketo and this email address exists in Marketo more than once, the most recently updated record will be selected for the list upload. Of course there is no telling whether that is the record you actually intended, risking incorrect data being reflected in your campaign for that person.

  1. Duplicates are magnets for extra duplicates

If you allow email duplicates in your database, it opens the door for other duplicate sources. Over time, this will create quite a mess in your database. An example: Your CRM sending a person to Marketo by its CRM unique Id will not be matched to a previously existing Marketo record with the same email address that does not have that CRM id.


So duplicates cause headaches, I get it. But what do I do about them? Unfortunately, there is no magic bullet here. Depending on your specific use case you need to simply make sure to manage them and keep the impact to a minimum. Some considerations:

  • Do you have a specific use case to allow the same person to be in your database multiple times? A good reason could be if your CRM contains the same person multiple times for multiple contracts, where you want to use Marketo to communicate with that person about each individual contract. You want both records with their details for that. That does mean however that you need to actively manage your unintended duplicates in Marketo to avoid them growing out of control. This case study shows how the situation can grow out of control and what it takes to solve that.
  • Is there no such use case? Then you may consider implementing a process in your CRM that only syncs the primary record for each email address. This will mean that profile information from your secondary records will not be available in Marketo. That is the price to pay for having your activities consolidated and keeping tight control over your duplicates. Alternatively, you could implement an external tool to merge duplicates regularly based on a predefined set of business rules.


Whatever your use case, it is well worth checking the system smart list called Possible Duplicates regularly to understand what is going on. As mentioned, there is no 100% solution, but by managing the process you can limit unnecessarily cluttered processes.

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