Windows 11 outlook: login name is not e-mail address

I do no longer seem to be able to connect Outlook to the mailserver.

My mail server requires a login name, not an e-mail address. To login to the IMAP server, I need to use name and not name@mailserver.nl.

Is it possible to use a username that is different from the e-mail address, and, if so, how do I configure that?