(I struggled with a title for this,)
We are running GroupWise 2012 SP2.
We have 9 post offices under one domain. One post office for each company under our parent. Each post office has a different internet domain name associated with it.
One of the companies is no longer part of our organization. They now have a new non-GroupWise email system outside of our system.

We have successfully migrated all of the users and their messages in that post office to the new service.
We would like to keep the old accounts active but hidden in GroupWise for a few weeks until everyone is certain they got all of the messages moved and no longer need access to our system.
Therefore, we set each of the users GroupWise users in that post office to Visibility = None.
We also had all of our users check their address books for any of those users and delete/re-setup them up with their new email addresses.

Everything is working great except replies. When a user from the company that left sends us an email and we reply, GroupWise is trying to send it to the old internal mailbox instead of following the return path or reply to path. Yet, we can send original emails to them without any problems.

The domain name associated with that post office has been removed from our system. We have done rebuilds on the users, post office and domain. We tried expiring the users. None of these solved the problem. Any ideas?

I tried to find a way to forward all of the users in that post office to the outside system, but didn't come up with anything.