We have a client on Server 2008, with on-prem Active Directory in addition to Azure AD, with Azure AD Connect syncing from AD to AAD.
Users have various licences assigned in AAD, along with teams, outlook (Inc. Shared Mailboxes) and so on.
A new Server 2019 stack has been built, which includes a rebuild of AD. I now wish to sync this new on-prem AD with the existing AAD tenant. The docs suggest this isn't possible, though we need an alternative solution.
Despite meeting the requirements for a softmatch in AD sync (Matching UserPrincipleName & ProxyAddress) i can not get this to work. The error shown is InvalidSoftMatch, "attributeConflictName" is "Mail". I have tried populating the Mail field in local AD to match what's in AAD but this throws a different error that the values must be unique.
If i delete a user in AAD, i can re-sync and this will create a new account in AAD based on the AD values, however mailboxes, onedrive, teams etc etc are not re-mapped.
I have tried setting mS-DS-ConsistencyGuid to the same value as exists in the 2008 AD, and running a sync, but the same errors as shown. mS-DS-ConsistencyGuid is set as the source anchor in both the 2008 and 2019 stacks.
Any advice on the best way forward with this would be greatly appreciated!