What is the issue?
The error is always DNS-specific. For this example, the domain gmbh.salzburg.at does not have any MX records assigned; it's a non-existent domain. When a domain lacks MX records, email servers do not know where to send emails to for that domain.
How to check the MX Record?
You can check the MX record online using website: https://mxtoolbox.com/
MX Loop-up result will be like:
What should the document sender do for Error code:498