Azure AD Connect sync: Attributes Writtenback from Azure Active Directory

These attributes are written back from Azure AD to on-premises Active Directory when you select to enable Exchange hybrid. Depending on your Exchange version, fewer attributes might be synchronized.

Attribute Name	User	Contact	Group	Comment
msDS-ExternalDirectoryObjectID	X			Derived from cloud Anchor in Azure AD. This attribute is new in Exchange 2016.
msExchArchiveStatus	X			Online Archive: Enables customers to archive mail.
msExchBlockedSendersHash	X			Filtering: Writes back on-premises filtering and online safe and blocked sender data from clients.
msExchSafeRecipientsHash	X			Filtering: Writes back on-premises filtering and online safe and blocked sender data from clients.
msExchSafeSendersHash	X			Filtering: Writes back on-premises filtering and online safe and blocked sender data from clients.
msExchUCVoiceMailSettings	X			Enable Unified Messaging (UM) - Online voice mail: Used by Microsoft Lync Server integration to indicate to Lync Server on-premises that the user has voice mail in online services.
msExchUserHoldPolicies	X			Litigation Hold: Enables cloud services to determine which users are under Litigation Hold.
proxyAddresses	X	X	X	Only the x500 address from Exchange Online is inserted.