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LeaCharnley
LeaCharnley
Level 3
March 24, 2026
Solved

Custom De-dupe issue

  • March 24, 2026
  • 2 replies
  • 26 views

When our instance was set up back at the start of 2023, we requested a custom de-dupe based on first name, last name, email address. All three fields have to match otherwise a new record is created. 

We have an API integration with our CRM. Any newly created or updated records are batched into a CSV which is sent via the API to be absorbed by Marketo. 

At around the start of February, I noticed that leads with the same email address, but different names were no longer matching for an update, instead, the names were being overwritten (in some cases actually creating duplicates).

Does anyone have any idea what might have happened to cause this? It has to be at the Marketo end, as we are not doing any matching, the API is just sending up a CSV.

I have a ticket open, but support have suggested the issue is with our CRM. This simply cannot be the case.

Best answer by Darshil_Shah1

I’d take a step back on the assumption that this is purely on the Marketo side, as what you’re describing usually comes down to how the API call is configured, not just the dedupe rules. For example, even if you had a custom dedupe rule set up initially (First Name + Last Name + Email), the API can override that behavior depending on how the call is made. Example: If the API uses lookupField=email, Marketo will match based on the email, and AFAICT, if the same email comes in with different names, it will update the existing record and overwrite values.

 

In order to have the API honor the overridden dedupe criteria, you need to OMIT the lookupField, and of course, ALWAYS include all the fields that are being used in the custom dedupe rule (email, first, and last names in your case), and it will create the duplicate as you expect.

 

I hope this helps. Pls let us know if you've any questions.

2 replies

Darshil_Shah1
Community Advisor and Adobe Champion
Darshil_Shah1Community Advisor and Adobe ChampionAccepted solution
Community Advisor and Adobe Champion
March 24, 2026

I’d take a step back on the assumption that this is purely on the Marketo side, as what you’re describing usually comes down to how the API call is configured, not just the dedupe rules. For example, even if you had a custom dedupe rule set up initially (First Name + Last Name + Email), the API can override that behavior depending on how the call is made. Example: If the API uses lookupField=email, Marketo will match based on the email, and AFAICT, if the same email comes in with different names, it will update the existing record and overwrite values.

 

In order to have the API honor the overridden dedupe criteria, you need to OMIT the lookupField, and of course, ALWAYS include all the fields that are being used in the custom dedupe rule (email, first, and last names in your case), and it will create the duplicate as you expect.

 

I hope this helps. Pls let us know if you've any questions.

LeaCharnley
LeaCharnleyAuthor
Level 3
March 24, 2026

Thanks Darshil! I will certainly pass that back to the integration team. The most confusing thing for me is that everyone is telling nothing has changed (either in the integration or at the Marketo end) so why would something that has been running successfully suddenly stop working.

Lea Charnley
SanfordWhiteman
SanfordWhiteman
Level 10
March 24, 2026

It would be weird (though not impossible) for the configuration to regress within Marketo.

 

Even if it would also be weird for your own code to regress, it’s simply more likely to be on your side since it has more moving parts. In line with Darshil’s suggestion, your team should debug with a direct (i.e. Postman/cURL) API connection.

LeaCharnley
LeaCharnleyAuthor
Level 3
March 25, 2026

Thanks to both ​@Darshil_Shah1 and ​@SanfordWhiteman. We took the lookupField=email out of the API call and it has indeed corrected the issue! 

Lea Charnley
Darshil_Shah1
Community Advisor and Adobe Champion
Darshil_Shah1Community Advisor and Adobe Champion
Community Advisor and Adobe Champion
March 25, 2026

Great. Thank you for posting the update, and glad that we were able to help you.

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