I have subscribed some iCal feeds on my zimbra calendar (e.g. tripit.com and doodle.com) as well as some other zimbra calendars of joint family calendars.
I mainly access my calendar through the CalDAV interface from my iPhone, iPad, MacBook and Mozilla Sunbird client.
While the zimbra calendars always are up to date, it seems that the ical subscriptions from the server calendar are not automatically refreshed. How do I ensure these calendars automatically refresh and where can I define the interval?