Unable to send the delivery to Hotmail and Outlook domains and working for others.
Status='Failed', Reason='Unreachable' and Text='501 5.5.4 Invalid domain name #ID#.eop-#DOMAIN#'.
Hosted and hybrid customers should contact Adobe Support to have the ‘.’ character removed from the end of the hostname in the PTR record for their sending IP. This ‘.’ character will always cause the domains like Hotmail to reject all messages from the IP with this “invalid domain name” bounce.
The initial Hostname in the PTR record was
rXXX.pXX.domain.net.. (rIP last octet.subdomain)
After removing that trailing ‘.’ the Hostname is
rXXX.pXX.domain.net. which should help to resolve the issue.
On-premise customers can perform this on their own if they are sending emails directly from their marketing instance hosted on-premise.