W2K server/Exchange5.5

What events are being logged in the event viewer?

There is a way also to have the services automatically restart. This is done thru services, click on the service/recovery.

But it is not normal for your exchange services to just stop. I would look in the event logs.

Also is this a hardened/protected box? Does it have the latest hot fixes installed.

Is 2k sp2?
Is exch sp4?

Have you run hfnetchk on the server to see if you are missing any HF's?

Do you only allow tcp 25 to connect to your exchange server from the outside, or is it open for any service? Do you have OWA also running on that machine (a no-no BTW).

I see two things for you to check with the limited information you provided:
1. "built from scratch" -- Exchange can be picky about the host hardware being on the HCL. Check your components against Microsoft's Hardware Compatiblity List.
2. Another possibility is an interaction with antivirus software on the server. We have an Exchange 5.5 on a Win2000 running McAfee Groupshield for Exchange that saw the same problem with the Exchange services stopping. We switched from using ESE (newer technology) to AVAPI (older technology). We think it might be the scan method because the services are staying up (at least in the short term). Good luck!