[exim] Layout of the exim spool directory

Hi.

Does exim make any assumptions about the partitions where /var/spool/exim
(assuming this is the spool directory) resides on?
To be exact, when using split_spool_directory, can some of the directories
under /var/spool/exim/input reside on one partition, and some on another?
Or does exim assume it can do a simple link/unlink to move files between
directories?

Thanks.