I would define an email black hole (EBH) as an email address or a website, who receives email about an issue but does not answer (to the surprise of the sender). In this case, an EBH is the opposite of a spam server: it absorbes unexpectedly instead of emitting unexpectedly (or in the language of vector fields, spam functions as a source and EBH as a sink).
Some examples from my personal experience (all in Berlin):
- Once I wanted to go to the dentist of the university clinic. I used the email option of the clinic in order to make an appointment. They never answered.
- Once I wanted to complain about the problematic delivery of a newspaper and used their email form. I was never informed if anybody read it.
- Once I wanted to see a lawyer and used her email form. She never replied.
Which consequences has this behaviour? That almost everybody offers an email contact option (no matter if they actually support this option), because they don't want to give the impression that they don't move on. And one liar brings millions of others behind him.