Email Authentication panel the solution?

Disclaimer: I am not affiliated with Mailroute.net - they have a filter product that seems like a good solution for those of us using one or more shared servers. I have been instructed by the mailroute.net team to lock down my server to block abuse. https://support.mailroute.net/entries/26786863-Locking-Down-Your-Server Restrict access to your mailserver to our block of IP addresses: This prevents spammers or viruses from connecting directly to your server and transferring unwanted email. In our experience, many spammers store away old settings, so some will have your old MX record archived, and will use that. Others use portscanning, or simple guessing to find mail servers that are accepting traffic on Port 25. Locking down this port allows you to prevent this from happening. There is one potential "gotcha": if you do this, you need to make the appropriate accommodations for any mobile users you have who might be relaying mail through your mail server. Many of our customers will require these remote users to use SMTP authentication, or will add an SMTP service on a non-standard port (like 2525), and have their users connect there instead of Port 25. All MailRoute traffic will come from our block of addresses. It's a block of 8 Class C networks: CIDR notation: 199.89.0.0/21 Netmask notation: 199.89.0.0 with a netmask of 255.255.248.0 Address range: 199.89.0.0 through 199.89.7.255 Note for users on shared servers: Sometimes, if you're on a shared server, you may not be able to lock things down like this. If that's the case, we suggest that you set up a filtering rule on your server or on your client software that redirects any email from the outside that doesn't contain the MailRoute headers. Every message we process will contain a number of headers. One that's good to use for this looks like: X-Virus-Scanned: by MailRoute If that headers not there, the email didn't come through us. Given all the different email platforms and management tools, it's hard to provide a simple howto to help you do this filter, but the general idea is: if (email is from outside, and doesn't have the MailRoute header) then (move it into a spam folder)
I asked Hostgator how to perform these steps and they shut me down. - NO CAN DO
I think that the Email Authentication panel in cpanel could help me. I would like suggestions on how to do this. I am not prepared to dump Hostgator...Just yet. I am experienced with cpanel, but not with mail server lockdowns (obviously) :-) Thank you