black-holed spam

We get spam articles submitted to the journal: obviously out of scope, and with many LMM "tells". I have noticed an increase in prestigious-sounding second authors, but whose emails bounce. I have always assumed the first author is trying to look more legitimate without letting the alleged second author be aware of the submission. We don't usually worry about this, since we are desk-rejecting these papers anyway.However, lately, there has been a rash of submissions where the submitting author's email bounces. This effectively black-holes their submission, as there is no way for us to let them know they have been desk-rejected. But I am unable to determine a use case for this activity: cui bono?