GreenNet email setup

I have set up greennet emails ( someone@gn.apc.org ) many times in Thunderbird and in my mobile, but have trouble with Nextcloud. The auto setup won’t work, and inputting all the details just like my Thunderbird (where this email works) also doesn’t work. The auto setup just goes gray and appears to hang. There are no error messages (maybe there is linux comand interface for this email setup?)

Thanks!
Michael.