--On Tuesday, September 27, 2011 15:51 -0700 SM
At 14:51 27-09-2011, Hector wrote:
What would make of this "400 defer" response?
It's a temporary failure. Your MTA can retry delivery. Some
people are creative with status codes.
I am quite certain Hector knows that and knew that long before
seeing this particular code. I'd guess --but it is just a
guess-- that failure to use a standard (i.e., specifically
listed in 5321) code is part of some greylisting scheme,
possibly to avoid using any of those standard codes ("I'm going
to make you try again to see if you are serious about getting
the message through" is definitely not on the 5321 list) and
possibly as an intended trap for the would-be spammer who wasn't
smart enough to read and understand the text in 5321 that
amounts to "if you are a client/ sender and don't recognize the
code, only the first digit counts".
I imagine Hector's real question was whether anyone else had
seen this particular use of 400 before and if it indicates
greylisting or a server that was really, really, confused. If
that was the question, I, for one, haven't seen it, but I
discontinued surveying the reply codes received by my server
some years ago.
Hector, could you clarify what you wanted to find out from this