Also to play it on the safe side I would also install some DDOS software protection. Set a limit for the amount of connections before the IP is blocked by your software firewall. If the person is threating to DOS your server then I would just report them to the officials and get them shut down.
Software firewalls are good as the uplink the server has, they can also overload the system by trying to block a lot of IPs in short intervals. So a real DDoS mitigation is really the best solution, unfortunately that doesn't come cheap.It'd be smart to also install software and not relay on your hoster's system.
Hey, someone threatened to do DOS Attacks on our server. We have DOS Protection
DDOS Protection: TopLayer Networks
and I'm wondering if it actually works against all kind of DOS Attacks?