Event ID - 1016

Event Id1016
SourceMSExchangeIS Private
DescriptionNT User EFFH\backupexec logged on to Administrator mailbox, and is not the primary Windows NT account on this mailbox.
Event InformationThis is a normal event and it will be logged in the Event Log regardless of the level that the diagnostics logging is set to on the Information Store. For example a backup software performing backup at the mailbox level will cause Exchange to generate such events.
Reference LinksEvent 1016 Generated When You Open Mailbox or Schedule of Another User

XADM: Event 1016 Logged During Mailbox Manager Cleanup

XADM: How to View Windows NT Accounts that Access Mailboxes in Exchange Server

XADM: Event ID 1016 Message Is Not Logged When You Log on to Another Users Mailbox

A 1016 event entry appears in the application event log after you upgrade to Outlook 2002

How to monitor mailbox access by auditing or by viewing Mailbox Resources in Exchange Server

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