Have any changes on the server been done lately?
For instance is a newer version of the web server or PHP installed lately?
Surely something is logged but and that most probably not in the RoundCube log.
Tell me more about your server and the OS and control panel you are using:
- web server: Apache, nginx, a combination, something else?
- Linux: Ubuntu, CentOS, Debian, Redhat or some other?
- control panel: cPanel, Plesk, some other, no control panel?
What versions?
Best regards,
Tomi Crnicki
Croatia, Europe