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...

Thanks, although nothing has helped at all. I checked QRESYNC, it was disabled, then I tried to turn off body structure, same result. Even in log file there is nothing indicating the problem. Well, that probably means that I really have to look for other mail clients. Do you have any tips? Something free, up to date and with the same layout like any other modern e-mail client (not like Thunderbird with mail list upon the mail body.) Thanks

Hello, I hope Opera Mail is not dead yet. I was trying to find some alternative to it but it seems like there isn't any software as comfortable as Opera, at least for Windows. I'm using multiple accounts, most of them are using Microsoft e-mail services. For a long time Microsoft hadn't allowed IMAP for their services, only POP3, however since they are allowing to use IMAP I have some issues with the mailboxes. Sometimes Opera doesn't download all the mails or seems to be stack with downloading huge number of e-mails. It bothers me especially when some important e-mails are not downloaded and I have to go to the website to check the e-mail there. Moreover this problem seems to be indicated by icon of small yellow triangle with exclamation mark next to the account name, however I don't get any information why is that. No warning message or error message at all. I also use some other e-mail account which is not provided by Microsoft and this account seems to work just fine without any problems. So the problem appears only with Microsoft account. I also use Avast! free as an antivirus and all of my Microsoft accounts have SSL/TLS turn on.
Does anyone have a clue why is that and what shall I do to repair it? It is very annoying and since I can find worthy alternative to Opera Mail, I'm lock with this client not working perfectly. Thanks.