Email address history is a feature where previous email addresses are stored to prevent reuse within a specified period. This means that even though you delete user1@contoso.com, no other user will get this email generated for them until the specified number of days have past.
Enabling this feature will cause the service to store all email addresses in a database.
It is possible to fully limit the write access that the service has, by setting the below setting. This will cause cloud only users to be queued in a request queue, rather than the service changing the userPrincipalName and email aliases directly. This means that you need to have a service that fulfills these requests.
Do not enable unless you have a service that processes these requests:
Signing in...
You will now be redirected to sign in with your work account.
Access Denied
You have not been granted the administrator role. To get access to managing settings, please sign in with an account assigned the Bytt.Email - Administrator role, as described in the role assignment documentation.
Need consent to API
You have successfully signed into the web frontend, but behind the scenes there is an API that also needs consent in your tenant.
Please request an administrator to follow the installation guide: