Certain mail.protection.outlook.com mail servers will not communicate with our mail server.

DSchertzMT 31 Reputation points
2022-01-27T20:38:57.97+00:00

Cross-posted here from the Office365 question forum, as directed by a mod.

We have had an ongoing issue where two of our customers (with many, many users that we need to contact in their respective domains) cannot receive email from us.

When we send an email, we eventually get a "Delivery Delayed" email from our Exchange server.

After 48 hours, we get a NDR message from our Exchange server:

550 4.4.7 QUEUE.Expired; message expired

I have confirmed on our Exchange server that the emails sit in the queue until they hit the timeout.

I have been able to do a manual telnet email send from our mail server to one of these customers, without issue.

We can receive email from these customers, but they continue to not be able to receive mail from us.

I have double-checked all of our DNS and DMARC settings for our mail domain - all appear well.

We have ONLY had problems with these two customers, amid thousands of other customers, but we have no way of verifying if any of them are using Microsoft to receive mail for their premises.

One of the aforementioned customers opened a ticket with Microsoft about this, and were told that our DNS entry was the problem, but did not elaborate on what was wrong with it. I have double and triple-checked our DNS and DMARC settings, and can find no fault.

I have tried to contact the IT departments in these customer recipient domains (through a gmail account) so that they can whitelist us - but one of them had no effect, and I've not heard from the second yet.

I have used the Microsoft Remote Connectivity Analyzer and performed an Outgoing SMTP Test with no error or issues.

I'm at my wit's end with this, and would appreciate any insight anyone has or if someone had a similar scenario. Checking for similar issues has not come up with anything exactly like our problem. Thank you, anyone who has any input.

Dave

Exchange Server Management
Exchange Server Management
Exchange Server: A family of Microsoft client/server messaging and collaboration software.Management: The act or process of organizing, handling, directing or controlling something.
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  1. DSchertzMT 31 Reputation points
    2022-01-28T18:07:57+00:00

    I have found a solution to this problem:

    I have created a custom Send Connector for the two domains, ignoring the sub.domain.org entry in their MX record.

    I configured the Send Connector to only use the FQDN of domain-org.mail.protection.outlook.com and now both customers have confirmed receipt of email from our mail system.

    Hopefully this helps anyone that runs into the same problem in the future!

    Dave

    4 people found this answer helpful.
    0 comments
  2. Kael Yao-MSFT 37,496 Reputation points Microsoft Vendor
    2022-02-01T08:53:55.703+00:00

    Hi @DSchertzMT

    Glad to hear this issue has been resolved!
    Thanks for the sharing.

    However, due to a recent update in forum policy, the question author now is not able to accept their own answers.
    167143-09.png

    I have written a brief summary of this issue.
    Please feel free to accept it as the answer to the question to help other community members.

    Issue Symptom:
    Exchange On-premises server and cannot send mail to multiple recipients from two different domains that are using Exchange Online.
    After 48 hours, a NDR message is generated from Exchange On-premises server: 550 4.4.7 QUEUE.Expired; message expired
    Sending to other recipients doesn't seem to have problems.

    Solution:
    Creating a custom Send Connector for the two domains instead of using DNS records.

    1 person found this answer helpful.