You may have got the following error when using CU1 or CU2 with Exchange 2013 when the routing plugin for multi tenancy is being used.
2 smtp;532 5.3.2 STOREDRV.Deliver; Missing or bad StoreDriver MDB properties
Now there are a couple of reasons for this, which are well documented.
The first reason is if you have a mailbox that is hidden from the address book. You need to un-hide the mailbox.
Another issue that will cause this that isn’t well documented is if you are using Email Address policies that check certain things like custom attributes or organizational units (OUs). If the user is sitting in the wrong OU, and the address policy specifies they need to be in another OU, you will get this error.
Hopefully this will be fixed soon.