The following are some tools I'd like to note down that are handy when it comes to checking server configurations and security:
- IntoDNS: An excellent tool that checks your site's DNS configuration and reports any errors and anomalies. Really handy!
- MX Toolbox: This site offers a bunch of tools to check your mail server. This includes checking its DNS entries, response times and security aspects such as open relays etc. Additionally, you can also check if your mail server's IP address is present in any blacklists. Useful if you are running your own mail server.
That's it for now. Please recommend other tools that you find useful!