Well, my IMAP server has a Quota Limit, but Roundcube doesn't support it.
I use Plesk and Courier / QMail.
it's not round cube problem The IMAP is the problem if it's courier you need to have a parameter in the config file
and where to get the quota if it's By database (MySQL, etc..) or by maildirsize file in the maildir directory
in courier the line has to be:
on the imapd configuration file
IMAP_CAPABILITY="IMAP4rev1 UIDPLUS CHILDREN NAMESPACE THREAD=ORDEREDSUBJECT THREAD=REFERENCES SORT
QUOTA IDLE"
i'm speaking about courier i don't use another imap server