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Internet Related/Filtering/Firewall Thread, 450 4.7.1 NDR in Technical; Hi there, we're suddenly getting a lot of these errors: ----- The following addresses had permanent fatal errors ----- <******@wgp.com.tw> ...
  1. #1
    bodminman's Avatar
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    450 4.7.1 NDR

    Hi there,

    we're suddenly getting a lot of these errors:

    ----- The following addresses had permanent fatal errors -----
    (reason: 450 4.7.1 Client host rejected: cannot find your reverse
    hostname, []) <*****@wgp.com.tw>
    (reason: 450 4.7.1 Client host rejected: cannot find your reverse
    hostname, [])

    Nothing has changed with regards to IPs or email setup etc so can't understand why this is happening.

    Anyone got any ideas?


  2. #2

    AngryTechnician's Avatar
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    Pretty much exactly what is says: your external IP ( doesn't have a reverse lookup entry in public DNS, so many servers will reject the message as spam. I can't explain why it's not been an issue before as this sort of behaviour isn't new.

    If that is indeed your public IP, you need to alter your public DNS records so that something resolves to it. If that isn't your public IP, someone else is sending spam with your from address, and there's not much you can do about that.

  3. #3

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    I have been having the same issue since last Thursday. Logged a call with our ISP(RM) but still waiting on an official answer/call from an actual engineer!

    I have therefore done a bit of investigation as I am still able to get email through to a Hotmail account, this is showing me the complete email headers. Here is what I have found:

    RM are the owners of &

    The addresses are assigned to the following mail servers:
    Received: from mq3.ifl.net ([]) by COL0-MC1-F20.Col0.hotmail.com
    Received: from mq4.ifl.net ([]) by COL0-MC1-F7.Col0.hotmail.com

    mq3.ifl.net however resolves to and mq4.ifl.net resolves to

    The reverse dns on are correct and point to mq3.ifl.net/mq4.ifl.net respectively.

    Up until 1 hour ago there was no reverse dns for There is now a reverse dns entry for which points to mq3.ifl.net. still has no entry at this time.

    Interestingly, on an email from last week the headers show Hotmail received RM email from

    "Received: from mq4.ifl.net ([]) by COL0-MC2-F28.Col0.hotmail.com"

    The reverse DNS for is out.mq4.ifl.net.

    It looks like RM have been playing around with IP address and haven't sorted out the reverse DNS entries correctly. Their site is showing that they experienced a DOS attack last week. Maybe this is the reason?

    Hope this helps.

    If I get a useful update I will let you know.

  4. Thanks to barbossa from:

    AngryTechnician (19th March 2012)

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