[otrs] Webmail problem

Hi to all, I've been successfully using OTRS for about a month, and I recently installed the WebMail addon. All the available options are checked and properly configured (fingers crossed), but NO messages are displayed, although the total mail count is correct and I'm also able to send outgoing messages without problem (see also the attached screenshot). FYI, when searching emails, again the number returned is correct, but no mail is displayed. I'm using imaps and I've tried two different imap servers (one of them is imap.google.com) and I still encounter the same problem. Do you have any idea what may be wrong? Thanks in advance, Theodoros