Using New Outlook on Windows for professional communication and productivity
Dear björnandersson4,
Welcome to Microsoft Community.
According to your description, you are having trouble adding an IMAP account in Outlook. Please correct if I've misunderstood.
I know you have double-checked the IMAP settings (server address, port, encryption method) to ensure they match exactly what your email provider requires. There's possibilities that New Outlook has compatibility issue with your IMAP account. If that's the case, I feel really sorry.
Since we have a dedicated team working on the new Outlook client, in order to better help you and no longer waste your more time. I recommend that you ask for help from our dedicated team, where technical engineers specialize in these related issues, and experts will focus on inquiries to further assist you, for details, please kindly refer to: Contact support and provide feedback in new Outlook for Windows - Microsoft Support
Plus, have you contacted your IMAP email service provider about this situation? Let's hear what they say.
Looking forward to your timely response, I will continue to follow up on your question here.
Best Wishes,
Stan.L - MSFT | Microsoft Community Support Specialist