Ability to use external email provider that doesn’t have SMTP support
Some newer customer engagement platforms, such as Braze, do not expose an SMTP interface to trigger email transactional sends, but do have many other ways to trigger transactional comms. This is in line with a trend to move transactional comms to a channel preferred by users (SMS, email, in-app messaging) or as part of a flow that will attempt one channel then fall back to another in case of failure - the customer engagement platform will implement all of that logic.
We use Braze for handling all transactional and non-transactional communications with users. Ideally we’d continue to do this and be able to manage our templates all in one place. However, Braze doesn’t support SMTP so we will be forced to use a different provider for some transactional emails triggered from Auth0 (e.g. password reset).
I believe there are already features on the Auth0 roadmap to enable users to use phone numbers as a primary identifier (instead of email), increased flexibility to use non-SMTP interfaces will also be required for that.