12.35Why email-based duplicate rules aren't enough

Two Contacts:

john@example.com
john@example.com

might indeed be duplicate.

But perhaps:

shared inbox

is legitimate.

Meanwhile:

john.old@example.com
john.new@example.com

may be the same person.

So duplicate detection is business/entity-resolution logic.

Idempotency is transaction/replay logic.

Different concerns.