To what extent is a domain name similar to a trademark?

That's interesting: In order to assess the similarity between a domain name and a trademark, a Panel had a look at what they were used for: "Given the high degree of similarity between the services offered, the Panel finds that the domain name is confusingly similar to the Complainant's mark" (WIPO Decision D2005-0406, hun.com). This is a broad interpretation of UDRP article 4.a.(i), which implies to compare the nature of the signs rather than their function.