One slight additional note, the email address is also populated from our PowerShell adapters such as Office365 and Salesforce.
This is because we match users from these based on Email address and so in the ImportedUser table (for On-Premises customers) you'll see a field called "MapUsingEmailAddress" which is set to 1 for these and that ensures the email is brought in from those connections.
As both are often integrated with your AD you may find that most users have an email address populated however for those that don't, a business adapter is likely your best option.
(Anything expressed here is my own view and not necessarily that of my employer, Flexera)
If the solution provided has helped, please mark it as such as this helps everyone to know what works.
