I can envisage the explanation of the root cause. "example.com." is seen as for examples in documentation, and what is the case here appears, rather, to be pla

I can envisage the explanation of the root cause. "example.com." is seen as for examples in documentation, and what is the case here appears, rather, to be placeholder values in softwares that have not been fully installed and configured with the correct information for the company. This might not be the case, but it seems likely. And yes, the "invalid." top-level domain might have been suitable, although one might equally question the wisdom of an application that is sending mail (rather than complaining loudly) when its mail settings have not yet been configured.