Looking for some guidance. Or aspirin :-)

Situation: 10 mailboxes on a Courier IMAP server.
Multiple users on multiple locations, all sharing all mailboxes.

The aim is to use Outlook 2003.
Couldn't get that operational at all, so for the time being, we
settled for Outlook Express instead.

Synchronize accounts produces loads of 0x800CCC0F errors.
More specific: at quiet times, I am able to sync each mailbox
individually without any error.
Once I try to sync all accounts at once, loads of errors are
reported, on random mailboxes and even when I just finished an
individual sync.

I can access all mailboxes using Pegasus without any error.
(No, switching to Pegasus is not an option. Sorry!)
And no, even with Norton Internet Security switched off, the
problems persist :-)

Questions:
- Is this setup a very unusual one ?
- Is there someone out there, running a similar setup without
problems ?
- Any hints on the cause of these problems ?
Somehow all problems seem linked to Outlook / OE. But it is
rather unlikely that all users run exactly the same versions.

Thanks!

--
Kind regards,
Gerard Bok