Why did Server 5.1 break Roundcube Webmail ?

It appears that Server 5.1 doesn’t properly activate webapps for the two default websites.

This issue only effects roundcube installations upgraded to Server 5.1
Roundcube can be installed or re-installed on Server 5.1 without issue.

Quick Fix

To re-activate the webapp after upgrading to Server 5.1, run this command:

sudo /Applications/ start com.topicdesk.roundcube