Many admins probably wouldn’t know that there is a size limit set on mailbox rules. The default value in Exchange 2007 and 2010 is 64 KB. It may seem small but up until recently I never had a need to change this value at a global or user level.
Every so often, though, you come across a user that’s the exception rather than the rule… so to say. The only indication you’ll get that the user is over the limit is a warning on the user’s desktop when they attempt to create another rule via Outlook.
“One or more rules could not be uploaded to Exchange server and have been deactivated. This could be because some of the parameters are not supported or there is insufficient space to store all your rules.”
Using Outlook Web Access will present the user with a slightly different message. OWA seems to do a better job at a more descriptive error message and even suggests a resolution for the user.
“Outlook Web Access cannot save the rule that you specified. Either the rule exceeds the maximum size limit for individual rules, or all your rules together, including this rule, exceed the size limit for rules. Remove some conditions, actions, or exceptions and try again.”
If the user is unable, or in my case unwilling, to clean up some rules. You can hop onto an Exchange server via Powershell and change their Rules Quota limit.
As mentioned, the default limit is 64 KB. There is a hard maximum which is 256 KB. Any value up to 256 KB is valid to use. In the example below I select a user via their email address to increase their quota to the maximum 256 KB.
get-mailbox [email protected] | Set-Mailbox -RulesQuota 256kb
We can easily check the new rules quota size for the user with the below command.
get-mailbox [email protected] | ft RulesQuota
Microsoft Knowledge Base article