What I liked to do is the following. Create a restore area for groupwise on another volume (or even another server). You could load a PC as a server if you wanted to to save on hardware costs.
Then copy the entire post office over to that volume per the restore area instructions and set up rights as needed for the users.
Then we did an EXPIRE/REDUCE event. We started by telling the users well ahead of time that on a certain date, any mail older than XXX days will be deleted. But we told them that those messages would be available in the restore area, which they can view any time they like from their GW client.
Now the real idea behind the restore area is to let users restore messages from a restored copy of the post office, BUT if you name the folder that the restore area is in greater than 8 characters, the USER CANNOT RESTORE to their mailbox. This makes it a read only archive area so the user can see their old e-mails, the mail will be off the main volume/mailbox server, and the user cannot restore to their live mailbox.
Then you can decide how long to keep the PO folder (maybe keep it forever, 6 months, 6 months and then onto tape/DVD) whatever you want. It covers you in terms of freeing up disk space and setting some limits on users so they get used to limits, but it won't make them mad due to "losing" emails and you won't have to get mail back for the big boss or anyone else - they can do it for themselves.
This was one of my best brainstorms back when I implemented it. What do you think Marv????