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If you are using Veeam Backup & Replication to protect a Microsoft Exchange 2016 environment, you should not (yet) apply the Cumulative Update 5 (KB4012106) patch to avoid mailbox item-level recovery issue.
In the weekly newsletter, Veeam notes that a couple of customers who already upgraded to CU5 reported some restore failures in Veeam Explorer for Exchange, caused by the significant change in one mailbox database structure.
Veeam is going to update Veeam Explorer for Exchange to be able to parse the new blob format correctly, and they are planning to include the fix in Veeam Backup & Replication 9.5 Update 2. Until it, could be better wait to apply this Microsoft patch in your production environment.