If you run into an issue with Exchange 2010 where the four system mailboxes aren’t created correctly, you will eventually run across this article: http://technet.microsoft.com/en-us/library/gg588318.aspx. Be sure to note that the GUIDs specified in the examples are not necessarily going to be the same as yours. Check yours in ADUC, double-click the account and take it form the Last Name field. You’ll find this same article rewritten all over the web but nothing I saw was extremely clear in stating this and I lost some time, hence this post. Be careful.

In case the process is broken, the steps are as follows:
Delete the system mailboxes from ADUC or ADSIEDIT.MSC if you're feeling frisky. The four you're looking for are along the lines of (but not necessarily)
SystemMailbox{e0dc1c29-89c3-4034-b678-e6c29d823ed9}
SystemMailbox{1f05a927-af78-475a-aba4-fc281398eb54}
FederatedEmail.4c1f4d8b-8179-4148-93bf-00a95fa1e042
DiscoverySearchMailbox{D919BA05-46A6-415f-80AD-7E09334BB852}
In ADSIEDIT, go into Users and then find CN=name.
From a command prompt, run "setup.com /preparead" off the Exchange 2010 install disk and then run the following commands from PowerShell, taking care to swap the GUIDs below with yours:
Enable-Mailbox -Arbitration -Identity "FederatedEmail.4c1f4d8b-8179-4148-93bf-00a95fa1e042"
Enable-Mailbox -Arbitration -Identity "SystemMailbox{1f05a927-8668-4003-adad-9b80758e86db}"
Enable-Mailbox -Arbitration -Identity "SystemMailbox{e0dc1c29-89c3-4034-b678-e6c29d823ed9}"
Enable-Mailbox -Discovery "DiscoverySearchMailbox {D919BA05-46A6-415f-80AD-7E09334BB852}"
Then do this crap, again substituting GUIDs.
Set-Mailbox -Arbitration -Identity "SystemMailbox{e0dc1c29-89c3-4034-b678-e6c29d823ed9}" -DisplayName "Microsoft Exchange"
Set-Mailbox -Arbitration -Identity "FederatedEmail.4c1f4d8b-8179-4148-93bf-00a95fa1e042" -ProhibitSendQuota 1MB
Now you should get three results when you do this from PowerShell:
Get-Mailbox -Arbitration
And one result when you do this from PowerShell:
Get-Mailbox -identity Discovery*