mx01.hosting4real.net and mx02.hosting4real.net are our SpamExperts filtering servers. If your MX points to these MX entries, your email will get filtered with the professional spam filtering service by SpamExperts.
Emails are then redirected to the "original" MX record for the domain - so if you point your domain to an external IP, you have to update the "Destinations" settings in the SpamExperts interface (It can be accessed via cPanel), or you'd have to remove our MX records and use your own.
Setting MX entries wrong might result in your incoming emails being discarded.
Please keep in mind that you can only use our SpamExperts filter if you're hosting emails with us, it cannot be used for external mail servers.