getting this error 554 5.7.1 even after applying the workaround?!

i set up SMG which was working for some time untill one day the customer cant send any emails through the smg and is getting this error 554 5.7.1

i tried to uncheck the box for the "Reject connections where the domain provided at HELO and EHLO has neither an 'A', nor an 'AAAA', nor an 'MX' record in DNS." but still having this issue

i dont even understand this error? it says "The best solution is to have the owner of the IP addresses' DNS records add a PTR record to resolve that IP to a fully qualified domain name (FQDN)."

what do they mean? do they mean the customer sending exchange server doesnt have an A record and a PTR record? or does it mean the smg doesnt have an A and PTR record???