Our users UPN (User Principal Name) differs from their email address. When syncing AD with Azure AD Connect it pulls over the users UPN and defaults to their login address. The company wants the login to be the users email address, and not their UPN.
The following steps are to add the email address to the AD Connect sync to Azure AD, and then to allow the email address to be used as the login instead of the UPN.
Uninstall Azure AD Connect and all components in the wizard.
Reinstall Azure AD Connect and select ‘mail’ as the ‘USER PRINCIPAL NAME’