Partitions should be independent isolated logical splits of a singular resource however in VFire they are interdependent as only one outbound email address is assignable regardless of the number of partitions configured. This makes the logical line between partitions hazy for both operator and customer of a non-default partition within VFire especially when logging new calls via email as only one partition can be "the lucky responder" and the others must go wanting.
This functionality is already available. Outgoing email can be configured by partition from the Admin>Email Setting screen and selecting the Partition drop down.
Particularly if the partitions are disparate parts of the organisation...