Baz, are you able to setup a new server at all ? That would be the easiest option and once that is done the emails could be injected into the new ZCS installation. Just to check your current version please post the following output
Code:
su - zimbra
zmcontrol -v
For a list of the logfiles take a look at
Log Files - Zimbra :: Wiki, and in fact for V4 the file was /opt/zimbra/log/zimbra.log so check that for any error messages.