I have not run into this issue myself but I got the question from a partner. The questions was what would happen when deploying the CRM rule to a users inbox using the rule deployment wizard and the maximum amount of rules is being exceeded. After asking internally I somehow got an answer and were pointed to the "solution" below.

When using the wizard and a users inbox has the maximum amount of rules errors are returned:

  • Failed to save the rule to the user's mailbox
  • Failed to access the default store with administrative permissions for the

Microsoft CRM Routing Rules are not deployed correctly to all the users. This behavior occurs if the rules that are in your mailbox exceed a size of 32 kilobytes (KB). The rules size limit for mailboxes on all versions of Microsoft Exchange Server is 32 KB.

At the moment this is a limitation of Exchange server, not Microsoft CRM.

More information can be found on kb articles.
http://support.microsoft.com/kb/147298/en-us
http://support.microsoft.com/kb/241325/en-us