Although I doubt it will help much, you can try email addresses from the RFC:
On Fri, Feb 2, 2018 at 7:16 AM, Mayo, Bill <bill.m...@pittcountync.gov> wrote:
> We are having emails sent to Earthlink being intermittently rejected with
> the reason “550 ERROR: No or mismatched reverse DNS (PTR) entries”. We have
> done quite a bit of troubleshooting on this, and the problem does not appear
> to be on our end. I actually have logs that show 2 consecutive messages
> where the first one is accepted and the second one rejected. I also see “421
> Load too high” messages in the log from Earthlink when these happen.
> I am trying to figure out how to contact Earthlink to get some assistance,
> but am striking out with how to contact them. The have a special page if you
> are getting a “blocked by EarthLink” response, but that doesn’t apply here.
> There contact page has chat support that requires you to provide an
> Earthlink account. Does anybody know how to get in touch with someone at
> Earthlink that could actually help with this problem?
> Bill Mayo