Use iCloud+ Custom Email Domain with Outlook for Windows

Hi,

I´ve set up an iCloud+ Custom Email Domain with Apple and I wanted to use the custom domain also on the Outlook App for Windows, where my @icloud.com email address is also set up. The customer email domain works at icloud.com and also via the mail app for apple, I can send and receive mails from and to the domain. After the initial set up via the settings from icloud it got automatically added. The domain works like an "alias" for the @icloud.com email. The incoming mails are received/ and the outgoing emails are in the send folded by icloud.com. I tried to add the email as an additional mail account on Outlook, it did not establish a connection to the server. I tried to change the icloud account information via Outlook; selected iCloud account, then clicked on account settings, then manage profile, and the email account; I tried to change the email to the custom domain there, but received the same issue. Do you have any suggestions how to use the customer iCloud Email Domain on the Outlook App, so I can sent and receive mails from that domain?