Event ID - 1504

Event Id1504
SourceMSExchangeOMA
DescriptionCould not successfully parse the Authorization header. The user information is neither a user principal name (UPN) nor in a domain\\user format.
Event InformationAccording to Microsoft :
CAUSE :
This event indicates that the credentials provided for the user were not correct or were not in the proper format.

SOLUTION :
This could be a malicious attack. Take security measures in trying to track the browse source, and then potentially disabling the service temporarily.
Reference LinksEvent ID: 1504 Of Source ID:MSExchangeOMA

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