OK - here is my setup:
DL380 G1 NW6.5 SP 6 servers (two file, print, home directories, Pegasus Mail, LDAP, DNS, DHCP and so on), one ZENworks 6.5, one BorderManager 3.8. Amazing how well NetWare runs on a PIII 933 with 3GB of RAM - try and do that with a M$ server ;-). HP Procurve 4000m, 2424m, 1600m and Extreme Networks 14001 switches with several different subnets.
Workstations of both W2K SP5 (yes 4 with the rollup) and XP SP2 running the 4.91 SP3 Novell client. Most 100Mb - some wireless. Some are IP only, some IP + IPX all have LDAP enabled.
Three different network shared installs of Pegasus Mail (two on one file & print server, on on the other f&p). Mercury/32 running on an nLite version of W2K Pro inside a VMWare Workstation 4.5 virtual machine. Mercury/32 modules S.P,E,D,X,I with Clamwall + Sanesecurity and Spamhalter. Users can access local mail via IMAP using mail2web.com or with "smart phones" / PDAs.
Since I am not "POP" ing my ISP with Pegasus Mail (Mercury does check every 5 minutes - backup MX) my Pegasus Mail config is somewhat different. I have quite a few things modded with respect to the way Pegasus Mail runs and what users can [not] change.
A couple thoughts...
Is the troublesome workstation on the exact same client SP level as the rest i.e. 220.127.116.1161109 (yes all the numbers at the end do matter)?
Check the Novell client settings against a "working" workstation - have any settings been changed or updated?
Try uninstalling / reinstalling the Novell client on the problematic computer (see a pattern here? - I've been bitten numerous times with Novell client problems). Find a release that works for you and stick with it until there is a newer feature that you just can't live without is my recommendation.
Is SLP setup, and fully functional? If not - I strongly urge you to configure it or resolve any issues it may have before spending much time on other things.
Could the WSOCK32 setting in Pegasus Mail have anything to do with your problem? I have mine set to "on demand only" - don't know if this even matters...
What is the flow control setting of the clients and switch ports?
You could easily setup Mercury/32 to POP and deliver mail for you in a VM... not something to offer as a resolution to your problem but it does give you much greater flexability and control if so desired...
Do you know of the school?
Check your PM for additional info...