On Tue, 17 Jul 2007, Ned Freed wrote:
In fact there are plenty of cases where submissions intentionally accept
messages they know are undeliverable just so they can send back a DSN
later. (We routinely have customers set things up this way.) The usual
reason for this is to work around incompetent clients that fail to
display error messages correctly or consistently. (Such clients are, sad
to say, fairly common in some places.)
I've heard reports that Windows Vista Mail ignores 550 replies it receives
after sending the message.
It depends on when the error is detected. If the error is detected during
initial submission the user agent typically throws up a window containing
whatever message the server put out. (But not always - see above.)
The error message is frequently truncated by the MUA (one line of a
multi-line reply), or error replies to early commands are ignored in
favour of later ones, which are often along the lines of "503 Bad sequence
of commands" and therefore unhelpful to the user.
Grr.
Tony.
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