which indicates that the user does not exist on that server is called as?

An automated electronic mail message from a mail system which indicates that the user
does not exist on that server is called as?

A.
SMTP Queue Bouncing

B.
SMTP Message Bouncing

C.
SMTP Server Bouncing

D.
SMTP Mail Bouncing

Explanation:

Reference:
http://en.wikipedia.org/wiki/Bounce_message