Mail not flowing between two domains RRS feed

  • Question

  • (Internal DNS Server/Exchange Server) -----DMZ----(Cisco ASA)----Outside----(External DNS Server/hMail Server)

    My internal DNS Server is in domain internal.com and external DNS server in external.com. I can send mail from/to Exchange/hMail servers within the same domain, but what I want to do is, I want to send mail from internal.com to external.com and back.

    For this i have done the following tasks:

    1. Have made a conditional forwarder to Public Address of internal.com DNS Server
    2. Conditional forwarder to external.com domain on internal.com DNS Server

    All NAT is correct, even i can connect on SMTP port of Exchange server from Outside, and similarly from inside. Both DNS Servers have respetive MX Records for email servers in their respective domains. But i am still not able to send email from internal.com to external.com and back.

    Any help will be appreciated.

    Wednesday, August 8, 2018 6:26 PM

All replies

  • Hi,

    How did you set the send connector? If you are using the recipient domain's MX record or the smart host to send emails to internet?

    Is there any NDR bouncing back?

    Please ensure there is not an intermediate device to block the inbound/outbound message.

    For reference: Manually Configuring Your Exchange Server for Internet Mail Delivery


    Manu Meng

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    Thursday, August 9, 2018 7:43 AM
  • Hi

    There is a setting on the Cisco ASA that does a security check, try removing this check and see if mail flows.

    Hope this helps. Please remember to click “Mark as Answer” on the post that helps you, and to click “Unmark as Answer” if a marked post does not actually answer your question. This can be beneficial to other community members reading the thread.

    Tuesday, August 14, 2018 4:22 AM
  • Hi,

    Just checking in to see if above information was helpful. Please let us know if you would like further assistance.


    Manu Meng

    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 shareexplore and talk to experts about Microsoft Teams.

    Wednesday, August 15, 2018 8:42 AM