what errorlevel to use if x: does not exist?

I have drive X mapped to a computers c: across the network.
my batch file:
goes to the mapped drive,
creates \directory if does not exist
goes to \directory
copies *.zip from my c:

what errorlevel would I use if driveX does not exist?
this is an unattended backup from mstask and I need to make sure the files
are going across the network
and if for whatever reason the drive gets disconnected... someone needs to
know.
I am already using errorlevels 255, 12-18, 1,2,4
Thanks in advance.