We experience a very odd problem with IMAPS port on Zimbra. External connections to that port start dropping suddenly as if the port is not open on the server at all. This happens several times a day. The most strange thing is that different external locations behave differently - we can't connect from one location and cannot from the other.
We tend to think it's a routing or port filtering problem on our hoster but we would like to exclude Zimbra from the equation before we start bother hoster's tech support. Does Zimra have any kind of connection rate limiting/port defense functionality or this problem is completely unrelated to Zimbra?