Hector Santos wrote:
Consequently, a sender-SMTP MUST be prepared to handle codes not
specified in this document and MUST do so by interpreting the first
The meanings of first digits other than 2 through 5 are not defined.
First-digit "1" is mentioned, but not really defined.
For a completely unrecognized code, the client SHOULD ignore the code.
NO! This is untenable. A client CANNOT ignore the code, because SMTP
*demands* that a client send a command after the server has sent a
If a server sends:
666 Mail diverted to the nether regions of the universe
The client *cannot* simply ignore it, or you deadlock. The server is
waiting for the client to do something, and the client sits there doing
nothing. So the client HAS to react somehow.
Now perhaps in an ideal world the client could respond:
UHOH Dunno what the heck you mean
but that's alas not part of the standard. Therefore, the ONLY sane response
is a QUIT or a RSET.