In the last day or so, we start getting our emails rejected by a certain domain with the following message:
I'm sorry to inform you that the message below could not be delivered.
When delivery was attempted, the following error was returned.
Name or service not known.
The problem is that I don't know on which side is the "name or service not known".
We were able to send a couple of days ago.
Thank you so much for your help!