Storage limit for Mailbox & CalDav/CarDav

CalDAV & CarDAV
CalDAV and CarDAV have no limit on the number of calendars and address book.

Mailbox quota
With roundcube users have the ability to check the quota of the mailbox

email quota

Message when the emailbox reaches over quota
An email will be sent to the user when the mailbox is full at 75%.
When the email box is full any incoming messages will be rejected.