12.5External ID needs to be truly stable

Bad external ID candidate:

email address

Why?

Because:

john@acme.com

may become:

john.smith@acme.com

Now Mule might think:

new customer

and create a duplicate.

Better:

customerId
memberId
orderId
policyId
sourceSystemRecordId

Something whose semantics are:

“This uniquely identifies the business entity over time.”