The PureMessage Activity Monitor or ExchangeStoreScan.log contains the below error:
PureMessage store scanning has encountered an application error (details: 'Unknown error')
First seen in PureMessage for Microsoft Exchange 4.0
The Exchange Web Services (EWS) based store scan is attempting to access an unrequired item and causing a NullReferenceException error.
Download and install PureMessage for Exchange version 4.0.3 which has a fix for this issue.
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