I am not aware of any specifications which would prevent using mail hosts on toplevel domains. However, dotless domain names are currently prohibited by the IC

I am not aware of any specifications which would prevent using mail hosts on toplevel domains. However, dotless domain names are currently prohibited by the ICANN Board New gTLD Program Committee,[1] so actually creating one may be a challenge. 1. https://www.icann.org/news/announcement-2013-08-30-en https://www.icann.org/news/announcement-2013-08-30-en 2. https://serverfault.com/a/721929/61174 https://serverfault.com/a/721929/61174