Anyone knowns what are the limits for the N900 mail app regarding big mail boxes?

I have an IMAP account. It has 2.8GB, 160.498 messages sorted out in 273 subfolders (only 1-2 leves of recursion among folders).

When I reach some folders like Inbox, a number of Expunged messages shows up, and after that N900 mail app just clears the on-screen contents and I cant actually see the mails in that folder.

When I navigate to some folders with a smaller amount of messages, in the same Mailbox, I can access all mails.

I have reached the same limits on iPhone and BlackBerry before. N900 took more time and certainly suported more e-mails before its limit was reached. Now it did.

If I can figure out what is the limit maybe I can arrange my e-mails to avoid it. Or if I can tune up (increase some limits) the device to support por e-mail...

Any ideas?