The problem: A user running Microsoft Outlook 2007 SP2 and connecting to Microsoft Exchange 2007 receives the following error message:
Cannot add to the server Junk E-mail Lists, you are over the size allowed on the server. The Junk E-mail Filter on the server will be disabled until your Junk E-mail Lists have been reduced to the size allowed on the server.
Would you like to manage your Junk E-mail Lists now?
The cause: There is a limit to the combined number of entries allowed in the Blocked Senders, Safe Senders and Safe Recipients lists (a total of approximately 2000 in later versions.) Unfortunately, many users overload the blocked senders list. The blocked senders list is useless to prevent spam and should only be used for bulk mail lists you can't get unsubscribed from. Instead, set Outlook's junk mail filtering to High and trust addresses from valid senders that is placed in the junk mail folder.
Importing a list of blocked addresses from an older copy of Microsoft Outlook is not recommended, in part because these lists often are larger than 512K and Outlook crashes when trying to import them, but also because spammers change addresses so often that lists are outdated within a few months.
The solution: The user needs to clear most, if not all, of the entries in the Blocked Senders list. If there aren't many names on the Blocked list, remove entries from the Safe Senders and Safe Recipients list too, As a last resort, disable the option to add contacts to the safe senders list. On the Safe Senders tab, clear the Also trust e-mail from my Contacts check box.
If the problem persists, you may need to clear the Junk Email folder’s offline items by right clicking on the Junk Email folder, selecting Properties and clicking Clear Offline Items on the General tab.
Changing the limit
Microsoft imposed the limit to improve performance, as the lists are stored as a hidden property in the Inbox and duplicated to the local registry. Each time the users synchronize with the Exchange mailbox store, the lists are downloaded. The limit can be adjusted on the Microsoft Exchange server, by adding a new registry key value to the following registry key:
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\MSExchangeIS\ParametersSystem\ DWORD value: Type Max Extended Rule Size Value Data: the maximum size (in bytes) you want to allow