Webmail on server version 4 or 5

Running RC on Server 5 is absolutely no problem

Leo

Updating your system should follow a very logical and systematic approach to avoid downtime. If these steps are followed, migrating should be trouble and stress free. If not, it can be filled with absolute terror akin to your first personal landing of a high speed aircraft.

1. I know it is not necessary to remind you to have a proper backup and restoration program and plan in place. You would surely also know to verify that.
2. Make a list of all the application software, databases running at present on your system complete with the version numbers. Your configuration management should be spot-on. Map this to the required Application/software requirement. Where delta's exist, have your update plan ready and verify the stages of it. Verify that the required minimal functionality will still be there. Verify at roaringapps.com for compatibility. Check their websites.
3. Download the latest versions compatible with your new OS, verify functionality and tick of your list as you make progress.
4. Verify the present location and path for roundcube and note it down. Download the latest updated stable version. Check for functionality and changes on the site and readme files.
5. Check and backup server and server configuration. Bender is a nice utility to do configuration backups.
6. Stop all services except DNS and your Open Directory. Alternatively you can stop all services by moving the server app to the trash.
7. Download and update your OS.
8. Download and install server. Start all the services one by one.
9. Navigate to the downloaded and expanded directory of the new Roundcube version. In terminal, log in as the superuser. Follow the update instructions in the Update text file. If you do experience an update db problem, you might have to temporarily disable SIP. Dont forget to enable it again.

Voila

Leo

Roundcube can be easily added with this installer package:

https://topicdesk.com/downloads/tools/roundcube-for-os-x-server/