IMNSHO their logic is screwed. The MX records work as follows

Get me a list of MX records for the domain seanet.com [done]
Can I connect to highest priority MX record ?
Yes = try and send the email
No = try next MX record

Under Yes, if having trouble sending email , exchange server retries but because 
server can always connect to highest priority MX record, it will keep choosing to use 
that one until the message holding peroid for your exchange server times it out and 
sends the message back to the server.

The people at seanet.com need to block port 25 for their server with the highest 
priority MX record. this will then force the exchange server to use the next available 
MX record.

Whilst not exactly explained see

ftp://ftp.rfc-editor.org/in-notes/rfc2821.txt
and
http://www.rfc-editor.org

for a 452 error your sherver should be (and is ) reacting as follows

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 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-SMTP agents) must agree on the interpretation.  Each reply
      in this category might have a different time value, but the SMTP
      client is encouraged to 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.)

cheers
dean




>>> [EMAIL PROTECTED] 9/09/2003 11:28:04 a.m. >>>
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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