What are the use cases for the user.data.email field?

[dan]

I see the user.data.email field is used when it is present and user.email is not present. From the doc:

This field will be used as the email address if no user.email field is found. This field may be modified by advanced registration forms or the API. Setting this value to another account's email address allows that account to, in some cases, access information about this user.

What are the use cases for that field?

[dan]

It is useful in a few scenarios.

• When you have users that share an email address, but are in the same tenant and have distinct accounts. FusionAuth enforces uniqueness on user.email per-tenant.
• When your users have a username (such as an account number) as a main unique identifier, but need self-service account recovery.
• When you have duplicate email addresses in a legacy system and are migrating them to FusionAuth, whether they point to the same account or not. You can move the users over and address email updates or account merges later.

Not all email related functionality is available when using user.data.email, but common workflows like forgot password are.