Thanks for the quick answer. I googled the problem and it seems to be a known Linux problem with the DNS Server. As I do not have direct access on the server today, I will check it tomorrow when I am in the office.

Also make sure after the DNS issue is resolved that the IP or domain name the ERP is hosted on is allowed on the mail server to generate SMTP records. If it's a domain name you might need to add SPF(?) text records to your DNS server that indicate that mail can originate from another external IP address, otherwise your ERP messages will be inadvertently blocked by mail servers thinking there is some email spoofing occurring.