There is a subtal but crucial difference between IMAP and POP-3. Outlook will not `connect` an IMAP server to your 'personal folders'. I don't think Thunderbird will either.
Short story:
POP-3 stores and works with your email locally on your computer, e.g. in your personal folders.
IMAP stores and works with your email on the server so it is always available no matter where you log into your email from.
Long story :
POP-3: your email is stored on your computer in your 'personal folders' you only connect to the server to send or receive emails. If you create folders for sorting your email, it is all saved locally on your computer. POP-3 has the advantage of being a simpler set up. Disadvantage is that if you move email out of your inbox to another folder you can only read the email on the computer in which you saved it.
IMAP: your email is stored on the server, you edit, file, and sort your email online using your email client. Depending on your settings, temporary copies of your email may be saved on your computer for reading off line, you can also compose emails offline, however next time you connect they will be copied to the server before sending. If you create folders for sorting your emails, the folders and the emails in them are saved on the server. Disadvantages are the set up can be more complex. Advantages are that all your email, even the ones sorted into other folders can be read on any computer connected to the Internet and most likely using a Web mail interface. However if you manually move your email into a personal folder then the email can only be read on the computer the personal folder is on.
Hope this helps, the way Outlook is handling your email from an IMAP server is buy design. The intent of the IMAP server is to not store your email locally on your computer.