[otrs] Mails being POPed but not displayed in OTRS

Hi, I am facing an unusual problem with OTRS 2.4.6 - mails are being POPed from the mailserver but are not appearing in any queue (including Raw). Strangely, this is not happening with all queues - only some queues are misbehaving :) Has someone else also faced a similar problem and hopefully solved this? Best Regards, Saurabh Pande.