As far as I can see no changes are done for the CAPABILITY in GWIA IMAP since 18.5, there we added UIDPLUS however the NAMESPACE never was reported back in CAPABILITY since at least 18.0 so I assume this was not there before either.

Currently this is what can be reported back in the different forms for CAPABILITY

STARTTLS LOGINDISABLED AUTH=PLAIN AUTH=XGWTRUSTEDAPP UNSELECT XGWEXTENSIONS UIDPLUS

Thanks Rob for the response. It could be that the client I am using, has that requirement. This client has been updated recently to.

Does this mean that I have to open a request? Is this a big change or just a flag that has to be reported back from GroupWise

Reading the RFC 2342 you mentioned this will be a big change I think.. It sounds like this will make the split between the users mailbox and proxy mailboxes so for sure this is not as simple as just adding the NAMESPACE but a design issue in relation to the proxy mailbox

But thats how im reading it, you can always open a request 

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IMAP4 [RFC-2060] does not define a default server namespace. As a result, two common namespace models have evolved:

The "Personal Mailbox" model, in which the default namespace that is presented consists of only the user's personal mailboxes. To access shared mailboxes, the user must use an escape mechanism to reach another namespace.

The "Complete Hierarchy" model, in which the default namespace that is presented includes the user's personal mailboxes along with any other mailboxes they have access to.

These two models, create difficulties for certain client operations. This document defines a NAMESPACE command that allows a client to discover the prefixes of namespaces used by a server for personal mailboxes, other users' mailboxes, and shared mailboxes. This allows a client to avoid much of the manual user configuration that is now necessary when mixing and matching IMAP4 clients and servers.
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