Hi guys,

getting confused by inconsistent statements I'd like to ask you directly: Having three users A, B and C configured in Office 365 and introducing AD sync with password sync (no AD FS) from a local AD with exactly the same users A, B and C - will this cause problems? (UPN, mail-addresses, names.. everything is identical)

1. Will the Office 365 users be replaced by the local ones?
2. Will they be logged out when synchronizing they for the first time?
3. Are accounts merged or will work got lost?

Thank you very much for your help!

1) The object attributes will be replaced with the ones from the on-prem AD. If said attributes match, probably no issues.

2) No

3) They should continue working. But if for example the UPN attribute changes, there might be an impact for the end user. Passwords changes will be synced from on-prem as well, and if you want to have all users immediately start using their on-prem passwords, you can force a full password sync as described here: http://social.technet.microsoft.com/wiki/contents/articles/28433.how-to-use-powershell-to-trigger-a-full-password-sync-in-azure-ad-sync.aspx