12.3The easiest Salesforce idempotency mechanism: External ID + Upsert

Suppose source sends:

{
  "customerId": "C001",
  "name": "Acme"
}

Salesforce has:

External_Customer_ID__c

configured appropriately.

Then Mule uses:

Upsert Account
External ID = External_Customer_ID__c

First request:

C001 not found
→ INSERT

Retry:

C001 found
→ UPDATE

Result:

one Account

This is why Upsert is so useful for integrations.