Storage Expiry is enabled.
How can messages from a single mailbox archive be prevented from deletion?
clear the "Delete expired items from this archive automatically" check box in the archive properties
use the Tools > Disable Mailboxes option
mark the "Lock this category" check box in the Retention Category properties and restart the storage server
create and apply an EVPM initialization file with "NONDeletable=True" against the mailbox
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