Joseph Brennan writes:
> I don't have a Mailman recommendation, but the situation is worth some
> comment:
>
> Notice Gmail "blocks" with a 4xx temp fail, for a message they will never
> accept. That's a protocol violation. It's abusive.
This is unclear, and I lean to saying Google's interpretation is not a
protocol violation. RFC 5321 gives a specific rule of thumb for this:
It is difficult to assign a meaning to "transient" when two
different sites (receiver- and sender-SMTP agents) must agree on
the interpretation. Each reply in this category might have a
different time value, but the SMTP client SHOULD try again. A
rule of thumb to determine whether a reply fits into the 4yz or
the 5yz category (see below) is that replies are 4yz if they can
be successful if repeated without any change in command form or
in properties of the sender or receiver (that is, the command is
repeated identically and the receiver does not put up a new
implementation).
I interpret that to mean that if fixing a broken sender-side DNS (an
SPF or DKIM record) would allow the message to pass a 4yz code is
justified.
I can't speak to other 4xx fails without knowing what they are.
It might be more useful to block with 5xx, but I don't think Google is
technically wrong on this, and they may have experience that says that
this is better.
Steve
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