I created a simple Matching Rule in my sandbox called ReplayedReceipts on object Receipt__c that did an exact match on a single field MessageId.

There were no records of Receipt__c in my sandbox.

SFDC said my matching rule couldn't be activated:

You tried to activate the matching rule ReplayedReceipts for identifying duplicate records. However, we can't activate the rule because it defines an unusually large number of records as possible duplicates. Specifically, take a closer look at these fields:

Message Id

Edit ReplayedReceipts to include a field that contains more unique values, and then try activating the rule again.

But I had no records for Receipt__c - how could there be duplicates?

1 Answer 1


Turns out that I had 13,000 test Receipt__c with (mostly) the same MessageId value that I had generated in some volume test. These 13,000 records were in the Recycle Bin

  • SFDC Matching Rule activation algo clearly looks at records in the Recycle Bin (understandable, they could get restored)

So, I emptied the sandbox's Recycle Bin and tried activating the Matching Rule again

  • Matching rule still didn't activate❗

Turns out the recycle bin records have to be physical-deleted via a Support Case or natural waiting for the background sweeper SFDC process. Once this occurs, the Matching Rule was activated.

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