Yes, I did, however without any success. It seems like it is not only my problem, it is problem of all users of microsoft e-mail services, as I see in this topic: http://forums.opera.com/topic/2255/opera-mail-sometimes-messages-are-missing-from-imap-inbox
And what is even worse, I tried to switch to Thunderbird, however the problem seems to be the same. Thank you for your help. F**ing Microsoft...