Like most ISPs, apparently this one wouldn't know an RFC if it bit them in
the ass. The relevant portion of RFC821 is included below. If the box in
question was not supposed to accept inbound mail, it should issue a 500
series error. Likewise, listing as an Mx record a server which is not
intended to receive mail is um... something only an ISP would think is a
good idea.
4yz Transient Negative Completion reply
The command was not accepted and the requested action did
not occur. However, the error condition is temporary and
the action may be requested again. The sender should RFC 821
return to the beginning of the command sequence (if any).
It is difficult to assign a meaning to "transient" when
two different sites (receiver- and sender- SMTPs) must
agree on the interpretation. Each reply in this category
might have a different time value, but the sender-SMTP is
encouraged to try again. A rule of thumb to determine if
a reply fits into the 4yz or the 5yz category (see below)
is that replies are 4yz if they can be repeated without
any change in command form or in properties of the sender
or receiver. (E.g., the command is repeated identically
and the receiver does not put up a new implementation.)
5yz Permanent Negative Completion reply
The command was not accepted and the requested action did
not occur. The sender-SMTP is discouraged from repeating
the exact request (in the same sequence). Even some
"permanent" error conditions can be corrected, so the
human user may want to direct the sender-SMTP to
reinitiate the command sequence by direct action at some
point in the future (e.g., after the spelling has been
changed, or the user has altered the account status).
> From: "Durkee, Peter" <[EMAIL PROTECTED]>
> Reply-To: "Exchange Discussions" <[EMAIL PROTECTED]>
> Date: Mon, 8 Sep 2003 16:28:04 -0700
> To: "Exchange Discussions" <[EMAIL PROTECTED]>
> Subject: Delivery to Alternate MX Records
>
> Hi All,
> I'm a bit puzzled by something and I'm hoping that someone can help out.
> There's a particular domain, seanet.com, that we can't send messages to at the
> moment. Any message sent to this domain hangs in the IMC queue with the error,
> 452 4.3.0 Cannot write message to disk. According to this ISP's support group
> they've recently reconfigured their main mail server so it can no longer
> receive messages from the outside world, and I assume that the error we're
> seeing is a result of this reconfiguration. They further claim that our server
> should try to deliver messages to their second or third mail server, something
> it definitely isn't doing.
>
> So here are my questions. Should an Exchange server (5.5, by the way) try the
> next MX record after getting a 452 from the primary server, and are there any
> settings in Exchange that affect this behavior? As an additional philosophical
> question, does it strike anyone else as strange that they should deliberately
> put an essentially malfunctioning server at the address of their first MX
> record in the name of spam fighting and security?
>
> -Peter
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