It depends - what's the purpose of the mailing list? If it's for purely personal or household purposes (e.g. a group of friends/family) then it's out of scope b

It depends - what's the purpose of the mailing list? If it's for purely personal or household purposes (e.g. a group of friends/family) then it's out of scope by virtue of Article 2(2)(c). Otherwise it'd likely be in scope with the list admin being the data controller.