Solution: Use this workaround to manually define your server correctly before the app connects to the server and messes up everything:
- Select "new account".
- Enter a non-valid mail address; it's important that the server is wrong, or even better, non-existant. Use e.g. blabla@ballaballa.org.
- Retry 3 times with this address.
- After the third try, you will be given the possibility to go to the extended options menu and enter your server information manually. BEFORE YOU CLICK THE EXTENDED BUTTON: Change your entered address to your real one, as you won't have the possibility afterwards anymore and thus won't be able to send mail (strange as it seems)! In the extended menu, you now have the possibility to select "IMAP". Do as you wish and enter your server information as you know is right.