This is strange, since SpamHaus gave me no issues:
However, I saw this, which I believe may be the cause of this error:
Sadly, InfinityFree being a free service provider tends to result in spammers trying to abuse it. Such violations are usually quickly detected and dealt with, however in the meantime someone may have filed a report on many rf.gd subdomains, and SpamHaus decided to add the domain to its blocklist, which likely blocks all free subdomains under it too.
There is a process mentioned for trying to get it de-listed, but only the Admin could file it and he has mentioned he’s tried it in the past and they were quite hostile at him, so it’s unlikely it would get resolved:
You could try getting another free subdomain from services like eu.org which doesn’t seem to be blacklisted, or try getting your own domain. Unfortunately, I’m not sure there’s anything else you can do if you don’t want that warning to display.