[Dovecot] Suggested IMAP Directory Size..

Hi,

ive walked into a enviroment where the previous admin has being using pop and making the email clients leaving a copy of the mail on the workstation..

Now overtime these mailboxes (mbox format) have grown between 1,5 to 1,8 Gigs large

I want to convert all these mailbox to IMAP (only 15) and want to know whats the largested suggest folder size per user dovecot IMAP runs smoothly with good responce times..

I know the users also have large OUT LOOK pst files 4.5GIGs and wondering if I could also intergrate that into IMAP?

Please any feedback would be great on this topic..??