Custom email domain with icloud+ - how to have it as a separate account in Mail?

I have a custom domain (ravnand.dk) where I have migrated emails to iCloud+ This appears to work nicely, but it seems that all the iCloud related mails end in the same inbox in the Mail app which I do not want as I use the non-custom iCloud account for other unrelated things. I would like my iPhone to treat my custom emails as a separate account similar to how it worked when I was using another provider. I did not immediately see any help pages describing this when browsing the iCloud+ documentation. How should I approach this?