Hi, different Scott here bumping this old post because I'm trying to do the same thing as described here with Sitefinity 10 and it appears this is no longer supported.
We're upgrading from Sitefinity 8 and have millions of user accounts with duplicate emails all over the place and we're unable to clean them up at this time. In the backend settings the default provider has the requiresUniqueEmail = false, but then when the CreateUser method runs it still returns a status of "DuplicateEmail".
When inspecting the UserManager.Provider object it is showing the correct "default" provider, but the RequiresUniqueEmail variable is set as "true". When I try to inspect it or modify it in code the variable is set as ReadOnly and marked with the following flag: "Obsolete: Parameter is no longer used, email address must be unique".
How can I replicate the same functionality that we have now in Sitefinity 8 so that we can continue with our upgrade?