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The server returned status code 550 - Mailbox unavailable. The server response was: Missing RDNS entry RRS feed

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    I was running exchange 2016 CU11 and everything was working fine.  I just upgraded to CU16, restarted the server, made sure all services are running, and now I can NOT receive any external emails.  I can send external emails, but NOT receive. I can send and receive internal emails.

    I ran the test at: https://testconnectivity.microsoft.com/

    and that's how I get the error message :The server returned status code 550 - Mailbox unavailable. The server response was: Missing RDNS entry:

    Any idea's what is happening, I looked at all my settings and they all seem to be there, so not sure how to fix?

    I would greatly appreciate any help I can get. 

    Dan

    Friday, June 5, 2020 7:08 AM

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    Hi Dan,

    From the NDR message, this issue is related to reverse DNS record. Please check and make sure your reverse DNS record is set correctly, and matches the HELO/EHLO hostname used in the receive connector. You can contact the network provider to update the PTR record in DNS server.

    Regards,

    Lydia Zhou

    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.

    • Marked as answer by afacts Monday, June 8, 2020 4:30 PM
    Monday, June 8, 2020 2:35 AM

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    Hi Dan,

    From the NDR message, this issue is related to reverse DNS record. Please check and make sure your reverse DNS record is set correctly, and matches the HELO/EHLO hostname used in the receive connector. You can contact the network provider to update the PTR record in DNS server.

    Regards,

    Lydia Zhou

    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.

    • Marked as answer by afacts Monday, June 8, 2020 4:30 PM
    Monday, June 8, 2020 2:35 AM
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    Thanks for the response, that's what I thought as well, but I already have a Reverse DNS record in place.

    So after about 2 hours, mail just started working on its own, emails started flowing in.

    Dan

    Monday, June 8, 2020 4:30 PM
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    It's great that you can get useful information here. If you have any other issues about Exchange, please feel free to post in our forum.

    Regards,

    Lydia Zhou

    Please remember to mark the replies as answers if they helped. If you have feedback for TechNet Subscriber Support, contact tnsf@microsoft.com.

    Tuesday, June 9, 2020 1:25 AM