This issue has been resolved.
The Zimbra slowness issues that some experienced has been traced to email migration processes. Performance of Zimbra has started to stabilize. It is possible that there will be further periods of slowness through the weekend as migration tasks are completed. We apologize for any inconvenience that this has and may cause.
The IT Help Desk has received a number of calls about Zimbra webmail
latency issues. Information Technology Services (ITS) is working to
resolve the issue and apologizes for the inconvenience.