Consider the following scenario:

In this scenario, no processing occurs. Also, the Export-MailboxDiagnosticLogs cmdlet generates the following error message during the archiving:


ELC EWS failed with error type:

'ArchiveExchangeWebServiceNotAvailable'. Message: Archive EWS url is unknown.


When you install Exchange Server 2016 CU18 or Exchange Server 2019 CU7, a new parameter, DomainName, is introduced for the *-AuthServer objects. The value for this parameter is empty ("") after installation. However, if you run Exchange Hybrid Configuration Wizard (HCW) version 17.0.5494.0, the DomainName parameter is populated by a domain from the HybridConfiguration object. This parameter is introduced to enable multi-tenancy (1:N). Therefore, the HCW creates multiple ACS AuthServers (per tenant). This causes the process of archiving "MRM / ELC" <MailboxAssistant> to Exchange Online archive mailboxes to fail. As a result, email messages can't be archived to cloud archives.


To fix this issue, install one of the following updates:

For Exchange Server 2019, install the Cumulative Update 8 for Exchange Server 2019 or a later cumulative update for Exchange Server 2019.

For Exchange Server 2016, install the Cumulative Update 19 for Exchange Server 2016 or a later cumulative update for Exchange Server 2016.


Learn about the  terminology that Microsoft uses to describe software updates.

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