Where is your mail store? What format?

I'm not sure I understand what you're asking. If you mean where is the
PST, etc. It's on the local HD.

Well, I was asking if your server was Exchange, POP3, IMAP, or whatever. If
you are using a PST file your server is using POP3.

The workstations are networked, so the thought is to regularly backup to
the server across the network or to a locla folder and then use a batch
file or local backup routine to copy to the server at intervals.

Well, it doesn't sound like you want to backup a server. You want to backup
your PST mail store. Outlook is a client, not a server.

As others have pointed out, normally you cannot backup a PST file if it is
in use. However, some of the third party suggestions sound interesting.
I've never tried any of 'em myself. I just copy the PST while it is not in
use for a backup.

-Frank