Synchronize AD to an existing Office 365 Tenant

Hey Mwkirk,

There is a good chance that you might loose the aliases you have added manually in office 365 account when you force a sync from on-premises. The behavior is sort of unpredictable on that part, in some cases i have seen them stay, while lost in other cases. The ones stamped by office 365 services for example SIP:user@domain.com, which is for skype, should still remain intact even after the user is synced from on-premises, for other aliases you added manually you can't say. Best is to first take out a backup of all the aliases you have stamped against the office 365 mailboxes : 

Get-Mailbox -resultsize unlimited | select Displayname,Userprincipalname,PrimarySmtpAddress,RecipientTypeDetails,@{Name='ProxyAddresses'; Expression={$_.EmailAddresses -join ","}} | Export-Csv MailboxEmailAddresses.csv -nti

Next you can test with one account to see if it retains the addresses.

Group synchronization should work fine.

On-premises exchange is not a hard bound requirement if you have never had one. You would be able to manage the attributes from users and computers, you can consider expanding the schema though for exchange attributes.

Even when you have all your ducks in a row, some users still might fail merging. And you might see duplicate accounts instead of one consolidated account. Ensure that the UPN, Primary SMTP address, Mail are not being used else where. If you are good on that part and still a user is failing to match, attempt a forced match after deleting the duplicate incorrect account completely:

Via command prompt on DC:

ldifde -f export.txt -r "(Userprincipalname=*)" -l "objectGuid, userPrincipalName"

This would give you the ObjectGuid for all the users.

Next you can stamp it against the user:

Set-MsolUser -UserPrincipalName User@domain.com -ImmutableId ObjectIDobtainedAbove  

Run a full sync.

Thanks