How do you know that email doesn't exist?
No way. Postman is not obliged
to comply with postal standards, it is recommended
to do it. But due to the fact that such "checked" divorced, like cockroaches in the apartment drunk, very often, on assectella users (as well as dismissed, etc) - go to the special user. This may be a regular user box which is cleaned daily or /dev/null. Mailer letter received. And gave it to /dev/null. From Your point of view - the box is. But really - its not :)