UPDATE (RESOLVED): All Zimbra webmail services for our customers hosted on the affected server should now be working.
We have identified an issue with a drive on one of our Zimbra servers, affecting the mailboxes on that server. The symptoms include: slowness, database errors, or continual loading screens. Our mail team is lessening the impact to affected mailboxes while the new drive is rebuilt.
Our mail team is working on repairing the down Zimbra server. While that server is down, load may be increased on the rest of the Zimbra cluster. UPDATE: The current ETR is 3-4AM