Current I am in the midst of migrating from Exchange 2007 to Exchange 2013. Almost half of the total mailboxes have moved. Now, A internal users attempt to send mail to Exch2007 would get the error - 9667:
Failed to create new named property for database "First Storage Group\Mailbox Database" because the number of named properties reached the quota limit (8192).
User attempting to create the named property: "Network service".
Named property GUID: xxxxxxx-xxxx-xxxx-xxx
Named Property name/id: "LastMessageWordCount".