Today the new version of "IBM Connections Mail" is available on the ICS Catalog, which will also support IBM Connections 5.
There are some new features like:
- Accept/Decline calendar invites
- Save messages as draft
- Adds support for Domino encrypted mail
- Adds direct access to the Microsoft Outlook Web App
- Adds support for Microsoft Exchange 2013
You can see some screenshots on the blog of Luis Benitez.