Contact Microsoft about this problem. http://answers.microsoft.com/en-us/outlook_com/forum/oemail-osend/imap-throws-error-9-server-error-when-fetching/0c3bbff0-75c8-4a40-ba60-7669fb7da659

Microsoft reproduced the same issue and after several days of troubleshooting concluded that the issue is with Thunderbird even though it says server error 9. It was confirmed after I installed Opera Mail and Mailbird and both cases Outlook.com IMAP worked flawlessly. There has to be something different about Thunderbird.

There was a reason I linked the MS support thread above. Please read it.

I have read the article but it is not helping me. I guess I am not seeing what you are trying to get me to see. There does not seem to be a resolution in the article. BTW: I do not have a large folder. I have around 2000 messages in my Inbox. Someone mentioned being able to reproduce the issue with OpenSSL and it may very well be a Microsoft issue. I am just trying to reason with the fact that I can use Opera and Mailbird without any problems and so they must have done something to get around the issue that Thunderbird is experiencing with Outlook.com IMAP service.

I'm not using Outlook.com, and I can't offer a solution either. What I understand from the article is that the issue is with Microsoft, and not specific to Thunderbird. As a workaround I'd reduce the number of messages in your Inbox. Also see http://kb.mozillazine.org/Keep_it_working_-_Thunderbird

In addition make sure not to let your anti-virus software scan your Thunderbird profile folder. And don't let it scan incoming and outgoing messages or attachments.