Emails to me are intermittently rejected by FreeToastHost. Maybe since 2019?

I am a member of Park Avenue TM in New Jersey (which should be in my signature). The problem happened Nov-Dec 2019, 2020 and recent months; it's almost a seasonal pattern. I have a small, website hosted by HostGator. I want to use an email address with that domain name to receive TM emails. As far as I know, only FreeToastHost rejects (bounces?) emails that I'm supposed to receive. One recent message that's typical says: "neubauer@coremetricsenergy.com appears to be an invalid or non-working recipient email address. (No advertised SMTP servers are accepting mail.)"

I've spent quite a few hours trying to troubleshoot this with HostGator. I provided them with files and email header information, which I can forward to you. I'd like to get rid of this problem permanently.

Hostgator is notorious for hosting spammers and many of it IP ranges have been blocked permanently.

I have opened your advertised email IP 192.185.36.120.




 

Setting aside for the moment HostGator's reputation (I've had very positive experience with them), would the change Brian has made prevent related error messages and email handling problems as long as I continue with the same HostGator account? I'm sharing a server with other HostGator accounts, and was assigned the IP address he found.
As I pointed out, the problem is intermittent, and it will take a long time before I have enough time to confirm that the problem seems to be solved from my end. If this thread is left open indefinitely, that seems best to me.
Thank you,
Franklin Neubauer

It should be ok until the IP address of your mail server changes.