While this is enough for the majority of users, some developers and a few users would require more space to implement complex routing and e-mail filing mechanisms.
KB Article 241325 explains this limitation
However, the Microsoft Exchange team now promises that this will change with E12, the next version of Exchange. An Exchange admin would be able to change the limit. There will be some tradeoff in performance for increasing the limit beyond a certain level so Microsoft has yet to determine what the default for this setting.
