MSExchangeIS Public Store
firstname.lastname@example.org failed an operation on folder /O=ORG/OU=FIRST ADMINISTRATIVE GROUP/CN=RECIPIENTS/CN=OAB VERSION 3AD24215E446FED006D7E903A387A01BE4002721 on database "First Storage Group\Public Folder Store (SERVER)" because the user did not have the following access rights:
'Delete' 'Read Property' 'Write Property' 'Create Message' 'View Item' 'Create Subfolder' 'Write Security Descriptor' 'Write Owner' 'Read Security Descriptor' 'Contact'
The entry ID of the folder is in the data section of this event.
This is a Warning message only, and according to Microsoft can be safely ignored.
You can change the amount of logging in MSExchangeIS\Public\Access Control, using the Exchange System Manager.