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NDR for some email addresses from a domain RRS feed

  • Question

  • Hi all,

    Exchange Server 2013 with MailScanner gateway.

    There are some email addresses from a domain that when replied to return an NDR.  Here is the NDR detail (sanitised):

    The recipient's email address isn't correct. Please check the email address and try to resend the message. If the problem continues, contact your helpdesk.

    The following organization rejected your message: au-smtp-inbound-2.mimecast.com.

    Diagnostic information for administrators:

    Generating server: <OUR MAILSCANNER SERVER>

    <RECIPIENT EMAIL ADDRESS WHICH IS 100% CORRECT>

    au-smtp-inbound-2.mimecast.com

    Remote Server returned '<au-smtp-inbound-2.mimecast.com #5.1.2>'

    I have checked the MailScanner logs and have found the following (again sanitised):

    civic-mailscanner01 sendmail[11791]: w9B62M3t011759: to=<SANITISED EMAIL WHICH IS DEFINITELY CORRECT>, delay=00:00:04, xdelay=00:00:00, mailer=esmtp, pri=240144, relay=au-smtp-inbound-1.mimecast.com. [124.47.150.222], dsn=4.3.0, stat=Deferred: 451 Internal resource temporarily unavailable - https://community.mimecast.com/docs/DOC-1369#451

    civic-mailscanner01 sendmail[14003]: w9BNe7iW013578: to=<SANITISED EMAIL WHICH IS DEFINITELY CORRECT>, delay=00:04:12, xdelay=00:00:00, mailer=esmtp, pri=211955, relay=au-smtp-inbound-2.mimecast.com., dsn=5.1.2, stat=Host unknown (Name server: au-smtp-inbound-2.mimecast.com.: host not found)

    The recipient email domain is @sa.gov.au.  The thing is only some email addresses when replied to generate this NDR; most are successfully sent.

    I have run our domain through mxtoolbox.com and we are not on any blacklists.

    Can someone advise where the issue may lay, or where else I may look to further troubleshoot?

    thanks

    Jus

    Friday, October 12, 2018 12:51 AM

Answers

  • Hello , 

    This seems to be a generic DNS related issue .Please make sure your E-mail gateway configured with your DNS server is able to resolve the domain name bigpond.com to get the relevant MX related to send E-mails .


    Thanks & Regards S.Nithyanandham

    • Marked as answer by juscopl Thursday, October 25, 2018 12:09 AM
    Thursday, October 18, 2018 9:04 AM

All replies

  • Hello , 

    I understood that you have problem in sending emails to the users in particular external domain .

    Below line is the snippet which i have taken from the NDR.

    " The following organization rejected your message: au-smtp-inbound-2.mimecast.com. "

    This issue seems like when your smart host tried to deliver the message but it is been rejected by the remote server for some reason .

    You need to find out why the remote server is rejecting the message which is sent from your organisation .Set up a call with the administrator who belongs to remote side and get this issue clarified .Moreover the Smart host product which you are using seems to be non Microsoft product .So on such case i would recommend you to involve the vendor of your Smart host product to have a look in to this issue.


    Thanks & Regards S.Nithyanandham

    Friday, October 12, 2018 8:21 AM
  • Hi,

    The error 5.1.2 generates because one of the servers on the way to the destination is unable to resolve the domain name of a recipients email address. The servers include Exchange server, smart host and ISP.

    Based on my searching, some issues with same error are related to sendmail problem. As Nithyanandham suggested, you can check the configuration of the smart host or contact with the vendor of it.

    Also, you can refer to the thread, try the solution there and check the results.

    Sendmail Error 550 Host Unknown

    Please note: Since the website is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information. And the changes made in the above blog is not supported officially by Microsoft.

    Regards,

    Dawn Zhou


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

    Click here to learn more. Visit the dedicated forum to share, explore and talk to experts about Microsoft Teams.

    Monday, October 15, 2018 8:55 AM
  • Hello , 

    i am writing to see how is everything going ? did you had a chance to talk with the administrator who belongs to remote side ?


    Thanks & Regards S.Nithyanandham

    Wednesday, October 17, 2018 7:25 AM
  • Hi all,

    Thanks for the replies.  Sorry have been busy elsewhere to get back to this.

    Have been getting the same error for some bigpond.com addresses.  But only some.  Will see the following in maillog:

    -------------------------------------------------
    Deferred: 451 4.4.3 <EMAILADDRESS@bigpond.com> recipient rejected. Mailbox unavailable, please try again later

    sendmail[3760]: w9HN89LZ003092: w9HNEJuC003760: DSN: Host unknown (Name server: extmail.bigpond.com.: host not found)
    -------------------------------------------------

    If I get the sender to send it again it will work!  The email address is 100% the same in both cases.

    We'll successfully receive email from and send email to other bigpond addresses and sa.gov.au addresses.

    We've noticed the issue lessening over the last couple of days though.

    Thursday, October 18, 2018 2:28 AM
  • Hello , 

    This seems to be a generic DNS related issue .Please make sure your E-mail gateway configured with your DNS server is able to resolve the domain name bigpond.com to get the relevant MX related to send E-mails .


    Thanks & Regards S.Nithyanandham

    • Marked as answer by juscopl Thursday, October 25, 2018 12:09 AM
    Thursday, October 18, 2018 9:04 AM
  • Thanks,

    We had another sa.gov.au email bounce back today.  I ran dig from our email gateway:

    ----------------------------------------------------------------------------------------

    [root@ ~]# dig sa.gov.au mx

    ; <<>> DiG 9.8.2rc1-RedHat-9.8.2-0.68.rc1.el6_10.1 <<>> sa.gov.au mx
    ;; global options: +cmd
    ;; Got answer:
    ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 30943
    ;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 12

    ;; QUESTION SECTION:
    ;sa.gov.au.                     IN      MX

    ;; ANSWER SECTION:
    sa.gov.au.              62      IN      MX      10 au-smtp-inbound-2.mimecast.com.
    sa.gov.au.              62      IN      MX      10 au-smtp-inbound-1.mimecast.com.

    ;; ADDITIONAL SECTION:
    au-smtp-inbound-2.mimecast.com. 62 IN   A       103.13.69.122
    au-smtp-inbound-2.mimecast.com. 62 IN   A       103.13.69.222
    au-smtp-inbound-2.mimecast.com. 62 IN   A       124.47.150.222
    au-smtp-inbound-2.mimecast.com. 62 IN   A       124.47.150.26
    au-smtp-inbound-2.mimecast.com. 62 IN   A       103.13.69.26
    au-smtp-inbound-2.mimecast.com. 62 IN   A       124.47.150.122
    au-smtp-inbound-1.mimecast.com. 96 IN   A       103.13.69.222
    au-smtp-inbound-1.mimecast.com. 96 IN   A       124.47.150.222
    au-smtp-inbound-1.mimecast.com. 96 IN   A       124.47.150.26
    au-smtp-inbound-1.mimecast.com. 96 IN   A       103.13.69.122
    au-smtp-inbound-1.mimecast.com. 96 IN   A       103.13.69.26
    au-smtp-inbound-1.mimecast.com. 96 IN   A       124.47.150.122

    ;; Query time: 0 msec
    ;; SERVER: 192.168.200.11#53(192.168.200.11)
    ;; WHEN: Mon Oct 22 14:16:09 2018
    ;; MSG SIZE  rcvd: 299
    ----------------------------------------------------------------------------------------

    <strike>I have noted that all the returns are from au-smtp-inbound-2.mimecast.com.</strike>

    Had one today from a sa.gov.au address bounce from au-smtp-inbound-1.mimecast.com.

    I contacted mimecast but they weren't interested in helping.


    • Edited by juscopl Wednesday, October 24, 2018 4:36 AM
    Monday, October 22, 2018 4:19 AM
  • Thanks!

    After further investigation it does seem to be an intermittent DNS issue with our gateway.  Now to find the cause of the intermittency!

    Thursday, October 25, 2018 12:11 AM