Couldn't find anything about this problem on the forums yet, so I thought I'd give you guys a heads-up.
Not entirely sure whether this only affects Zimbra webmail in combination with Internet Explorer 10, but the following update kb2962872, which has been released this July, causes performance issues.
Afaik deleting emails, tagging emails and dragging emails to different folders is much slower after having installed this update. I don't know whether there are other actions which also suffer performance issues as well.
Seems this update has caused more issues with other applications, see https://connect.microsoft.com/IE/fee...kb2962872#tabs
Reproduced on Zimbra Community Edition 8.07 GA 6021 and Internet Explorer 10 with kb2962872
Internet Explorer 11 with kb2962872 seems unaffected