> Thanks Dan and Roger,
> I don't host majordomo and only have admin access to it via email.
> I'll obviously ask the host to create that file for me;
> If he can't / won't for some unknown reason, presumably I can't create
> that file on a url / different server and enter that link in the
> restrict_post function ?
No. Files must be local. URLs are not filenames; filenames are not URLs.
(You could create another list on the server, put those addresses in it,
put its name in the first list's restrict_post in addition to its own
name, and make the list moderated in case anyone tries to post to it...)