One of the options for how to handle mail that the default or catch-all email addresses of cPanel users receive. The blackhole option discards mail after the server accepts it. For this reason, it may result in additional spam that your users receive, and it places a larger load on your server than the fail option.

black hole|nodot=x|lang=en, especially in the attributive. (Internet) A place where traffic is silently discarded. (programming) A bit bucket; a place of permanent oblivion for data. (computin [..]