If a user receives a NDR with the following in the diagnostic data, establish a TeamViewer session with the user’s PC and deactivate unapproved third-party add-ins, such as Snag-it:
#550 5.2.0 STOREDRV.Deliver: The Microsoft Exchange Information Store service reported an error. The following information should help identify the cause of this error: “MapiExceptionNamedPropsQuotaExceeded: . . .
Many, if not all, Outlook add-ins add named properties, or X-headers to messages in Outlook. Exchange assigns IDs to the named properties. When the named properties IDs are exhausted, Outlook cannot map the named property, and the message cannot be delivered. Not all messages are affected, only those utilizing the add-in that cannot be mapped by the affected database.
Detailed info can be found here: http://technet.microsoft.com/en-us/library/bb851492(EXCHG.80).aspx