32G mailbox in IMAP to MAPI sync failure

[basictheprogram]

I have a user with a 32G mailbox (and folders) that was accessed via IMAP and things worked great.

Installed ZCO (for the additional feature set) on Outlook 2007 and the MAPI sync beat-up on the hard disk and made the system very slow.

After 36 hours of sync-ing the user exited Outlook and killed the sync.

I used ZCOLogCtl.exe and turned on all debugging and attempted the MAPI sync again. I'm at 7.5G of logs and counting.

Several questions:

1. What is ZCO/Outlook doing on that initial sync?
2. Where do I start troubleshooting this issue?
3. Is a MAPI the wrong protocol for a 32G mailbox?

I was under the impression that MAPI was a better protocol for Outlook and large mailboxes. Is this impression "wrong"?

The mail is split into many IMAP folders. None of the folders are larger then 1G (keep .pst files for being corrupted). Shouldn't MAPI, given enough time, sync things?

Looking for any advise or help.

Thanks.