IMAP path prefix

Hi,
I have tried zoho mail for a while and I am not satisfied with the service.
I have now set up a google apps account and tried to migrate all my emails from zoho to my google apps email account.
I have enabled IMAP in zoho and now when trying to configure the transfer I am asked for the zoho "IMAP path prefix".
I have not been able to find this information on the zoho support pages. I have tried several options such as "imap.zoho.com" , "/", "IMAP" and also "INBOX" as recommended elsewhere but none of them works. Even leaving the field empty does not work: whatever value I try for the "IMAP path prefix" google apps mail transfer service cannot get the folder structure I had set up in Zoho mail.
Could you let me know what value should be used as the zoho "IMAP path prefix"?

Thanks
Christophe