Why Roundcube shows zero in mailbox usage when Plesk shows non-zero usage?
This mailbox has got Unlimited mailbox size in Plesk > Subscriptions > example.com > Mail > Email Addresses > email@example.com > General:
In order to check that disk usage is calculated correctly perform the following.
- Change this value to limited one (e.g. 10 MB)
- Refresh browser tab with Roundcube (F5 for Chrome browser)
- Check the disk usage in Roundcube: