Unable to update this object because the following attributes associated with this object have values that may already be associated with another object in your local directory services: [UserPrincipalName email@example.com<firstname.lastname@example.org>;]. Correct or remove the duplicate values in your local directory. Please refer to http://support.microsoft.com/kb/2647098 for more information on identifying objects with duplicate attribute values
When implementing SMTP soft-matching after a cutover migration, you may see this error if objects in the on-premises AD were not properly prepared to sync.
To fix this, you need access the object in ADUC and set the “E-mail:” attribute to the primary SMTP email address of the user in Office 365. This is how SMTP soft-matching works.
Then run another sync and the on-premises AD account should sync up with the Office 365 account. For help with forcing a sync, please see this article: