I have a location which has been complaining about about the speed of Zimbra IMAP performance in Outlook. When deleting / moving a message it can often take 3-4 seconds per message. They have tested other e-mail services and they did not yield the same results. When a different client is used such as Thunderbird, or the Zimbra Client it is fast as lightning.

When looking through the mailbox.log I noticed the two different clients do things a bit differently and this is probably what's causing the issue. When deleting an e-mail via outlook, the log show the copy to the appropriate trash folder and then a Delete Message. However when the same task is done via Thunderbird, the logs just show a copy.

Here is an example in the logs of Outlook:
2012-12-28 12:12:52,263 INFO  [ImapServer-836] [name=imaptest@airxcel.com;mid=260;ip=;] mailop - Performing IMAP copy of Message (id=591): copyId=594, folderId=260, folderName=Test, parentId=-591.
2012-12-28 12:12:52,265 INFO  [ImapServer-836] [name=imaptest@airxcel.com;mid=260;ip=;] mailop - Performing IMAP copy of Message (id=592): copyId=595, folderId=260, folderName=Test, parentId=-592.
2012-12-28 12:12:53,552 INFO  [ImapServer-836] [name=imaptest@airxcel.com;mid=260;ip=;] mailop - Deleting Message (id=591).
2012-12-28 12:12:53,554 INFO  [ImapServer-836] [name=imaptest@airxcel.com;mid=260;ip=;] mailop - Deleting Message (id=592).
And here is Thunder bird doing the same action:
2012-12-28 12:11:41,826 INFO  [ImapServer-833] [name=imaptest@airxcel.com;mid=260;ip=;ua=Thunderbird/17.0;] mailop - Performing IMAP copy of Message (id=578): copyId=581, folderId=260, folderName=Test, parentId=-578.
2012-12-28 12:11:41,828 INFO  [ImapServer-833] [name=imaptest@airxcel.com;mid=260;ip=;ua=Thunderbird/17.0;] mailop - Performing IMAP copy of Message (id=579): copyId=582, folderId=260, folderName=Test, parentId=-579.
Any help would be much appreciated. The other location is trying to talk the Head Hanchos to switch to Exchange.

Release 7.2.0_GA_2669.RHEL6_64_20120410002025 CentOS6_64 FOSS edition.