The simplest solution would be an external storage box connected to your server. Various manufacturers make these - Promise is one that we have used in the past and found pretty reliable. I believe they make versions that have SATA hard drives instead of SCSI internally, which makes it very economical too. You can configure the external box to have various size hard drives, depending upon the mfr's specs, and I would definitely recommend getting one with mirrored drives at least if not a RAID 5 array. It connects to the server through an external SCSI connector, requiring you to have a SCSI controller in the server with an external connector. Make sure it's NT compatible, though, because obviously you know that you are working with a very outmoded operating system. I'm not sure about Exchange 5.0, but I know with 5.5 you could move the entire mailbox store to a different hard drive (on the same server of course) without too much trouble. As I recall, you just go to the appropriate dialog box in the Exchange Administrator program and specify where you want the mailbox store to be moved to, and the administrator program moves it automatically. Of course, you want to be sure to have a good backup just in case, and perform the move operation at a time when you have plenty of available down time just in case something happens. I believe the maximum partition size in NT was somewhere around 130GB (???) - maybe someone else would be more certain of this than I.
Hope this helps!
