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Some of my users are getting the "Delivery Status Notification (Delay)" messages in their inbox for mails sent to a single recepient. Here is what confuses me

I did the nslookup test and saw 2 MX servers. I was able to connect to one but not the other...both has 0 preference. I went over to dnsstuff to make sure and the result was

  • On first MX server: [Could not connect: Could not receive data: Operation timed out.]
  • On second MX server: [Successful connect: Got a good response [250 ok]] (took 0.500 seconds)

I am using IIS SMTP as a relay server for my exchange 2003, it acts as a gateway server. Why is it not sending the mail to the second IP to avoid the delay mails?...just curious.

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up vote 2 down vote accepted

Looks like one of their 0 weight mail servers are down. Servers with the same weight are round robin load balanced so when your mail server connects to that one it times out and if there are no higher weight servers then you get the NDR.

If you don't control the server you can either wait it out, or try and get in touch with the person who runs that server.

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I believe this might be the better option. – Saif Khan Feb 16 '11 at 16:15

Telnet to the second server on port 25

issue these commands





type some data here

end with a period and a few lines


See if their server is able to accept a message at all.

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I was able to open a connection, as soon I typed E it dropped the connection, trying to reconnect and unable to. – Saif Khan Feb 16 '11 at 16:14
This would indicate that not even their second server is working but it is able to connect so your server is set to retry and will continue to do so. – pablo Feb 16 '11 at 16:18

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