1. Traceroute – With this quick tool, you can trace the network path from your server to any destination, including your house. If you ever have connection problems with your website or server, this tool may give you clues.
2. IP Whois – Find out what a website’s true IP address is, where it originates, who owns it, and more.
3. Reverse DNS – Test reverse DNS to make sure your server is setup correctly according to Internet protocols.
4. SPAM DB Lookup – Is your website or server on the spam list? This tool will tell you if you need to do some housecleaning or beefing up of security.
5. DNS Lookup – Make sure all of your DNS records (A, CNAME, MX, and more) are setup correctly.
There are websites that have all of these tools available either for free or for small fees. You can also perform many of them from the Linux command line, if that is available to you.