A lot of us know this but for those who don't I want to add the appropriate information. Every website has it's own ip address. Hackers can use this to attack or DDoS your website holding it offline. DDoS stands for distributed denial of Service. What this means is the person attacking you can hold your website offline by sending packets from different bots in what they call a botnet. Which is basically a list of other infected computers used to make these bots that can then all be sent to your website in packets to attack and hold you offline. If you delete any trace of the MX entry on your website hackers cannot access your ip address and will have no way of knowing it. Just a tip for the new web master or the newcomer. This is very helpful information and I know this from experience, trial and error and dealing with being a web master for a little over 3 years now.