450 4.7.1 error client host rejected: cannot find your hostname


  • Hi,

    I know that there a lot of topics on this matter but i couldn't find the answer to my question.

    The error mentioned shows up send to one domain at this moment. Emails send from that domain can be received by our domain.

    As far as i can test my part it all seams to be ok. PTR is available (otherwise a lot of other domain would be returning a similar error)

    My guess is that their DNS is not updated but I want to gather some evidence and send it to them. If possible also send a solution for them as well.

    While my part is pretty much working my users will complain to me that they receive this error and they don’t want to hear that I can’t do anything and the other party should do some work.

    Also because mails from their side are arriving at our side they don’t see the problem.

    I hope you guys can help me out.

    Friday, March 9, 2018 9:08 AM

All replies

  • Hello,

    Thanks for contacting our forum. This normally means that the address you are trying to send email to, the server is using reverse look ups. This means you send an email from this leaves your system stamped with your IP address. Then when the remote system receives your email it does a check to see if “” is actually the sender by making sure that the IP the mail came from points to “”. This is done by querying the PTR record.

    So, if you see this error there are two things to check. First is the receive connector that issues the HELO/EHLO to verify the servers identity.  Make sure you enter the correct FQDN of the server.

    Then have a test for the PTR record and check if it’s successfully.


    set type=ptr


    Try getting your SPF record setup and also send a test email and check the results.

    Make sure your IP or domain name isn’t in any blacklist:

    Hope it helps.

    Best Regards,
    Jason Chao

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    Monday, March 12, 2018 2:24 PM