Zimbra Slow With Exchange and Other Questions

[g3neration]

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I have a mailbox about 1.5GB in size with about 70+k emails in INBOX, on an Exchange server. Judging from the forums, Zimbra should be able to handle this with no problems. Yet I've come across a few:

1) When connected via IMAP, it does not download all emails. So far its at 36+k and it just stops. Looked in logs but there doesnt seem to be any indications of a problem.

2) When Zimbra is syncing, it takes a very very long time for it to "finish" (upwards of about 10 - 15 mins on the local LAN). When it does finish, I do not notice all the "new" emails I'm supposed to get. This was verified by logging in via OWA.

3) Is there a way of adding other search engines?

4) I do notice that my calendar events get posted. But there are public folders that also have calendars in them that get "added" (I'm not sure on the correct term here) so that my calendar not only contains mines, but public events. Is there a way for me to sync that with Zimbra?

Any help would be great. Thanks.