The errors you’ve shown are normal, we don’t publish DMARC records and our email server doesn’t support TLS yet. But that should not prevent you from receiving email, and definitely should not return “Host or domain name not found.” errors.
I suspected that the problem might be caused by the nameserver issues going on: Ongoing Nameserver Issues But it looks like you’ve already implemented the workarounds proposed there, which should help.
When did you last update your nameservers? If you did so recently, then maybe the problem is already resolved?