Actually, the DNS entry is the same (18.104.22.168), as expected. It seems what's different is the vhost. Very likely, the server has one vhost for each server name, specifying the final dot for one of them and not for the other. It's more of an Apache question than a DNS question I think.
Now as others have said, the difference between
admin.to. is that the second one is a fully qualified name, so your resolver won't try to resolve it by appending your DNS
search parameters to it, whereas the first one will be tried with the
As an example, I put
raphink.info in my search path in
$ grep '^search' /etc/resolv.conf
$ getent hosts www
22.214.171.124 raphink.info www.raphink.info
$ getent hosts www.
The first request is
www without a trailing dot, so the resolver tries to solve it with the search path. The second request is a fully qualified name since it has a trailing dot, so the search path is not tried, and the resolution yields no results.
Now as I said, your question in this case seems more like an HTTP server thing than a DNS one, since I get the same result on my own machine:
$ getent hosts admin.to
$ getent hosts admin.to.