The original text in rfc2821 implies that reject and bounce
are the same. Search for "bounce" in rfc2821 and you see what
I mean; I'd like to highlight text from section 3.5.3 to defend
"... to the use of reply codes 251 and 551 ... that would be
forwarded or bounced...". Clearly, 251 is forward, 551 is bounce.
rfc2821bis suddenly changes the definition of bounce to become
an after-the-fact pseudo rejection. Section 6.2 for instance:
"If they cannot be delivered, and cannot be rejected by the
SMTP server during the SMTP transaction, they should be
"bounced" as described above."
I'd like to see this changed into "sending a DSN" (or something
similar) in stead of "bouncing". A bounce is like hitting a wall
(not getting in), not a notification message.