Very strange problem here. All of the sudden I get a call from a customer saying they can't get any emails and they're bouncing back. However, they are able to send out just fine. I do some testing and all emails sent to all domains are bouncing back with the following: (some user)@(some domain).com (550 5.1.1 <(some user)@(some domain).com>: Recipient address rejected: User unknown in local recipient table) I then checked through the posts on here with the same problem, verified the main.cf and virtualusertable and everything looked fine. I restarted ispconfig, restarted postfix, even restarted mysql to no avail. I checked the ispconfig log and found no errors. Then, out of the blue, they all start going through again. So at this time they are all working but I need to find out why they stopped working and why they all the sudden started up again. I'm afraid this problem may come back and there's no apparent reason why. Any thoughts?