A local loop was detected

Question

Hi All,

As I am upgrading the hybrid exchange server 2010 to hybrid exchange server 2016.

HCW was successful, receive and send connector seem to be fine on the exchange 2016.

First I could not send an email from @mycompany.com to external email (@gmail.com) after updating the TlsCertificateName on the Default Frontend Ex2016 from Receive connector Exchange 2016, now I am able to send out.

But I am not able to receive an external email e.g ******@gmail.com to ******@mycompany.com, from EAC message trace status: resolved and delivered, I checked the Queue Viewer on the Exchange 2016, the email was stuck in the queue with the last error: A local loop was detected.

I have been troubleshooting but nothing helped.

would anyone please help me with the issue that would be much appreciated.

Best Regards

Answer 1

Hi @vdz ,

Great to know that the issue has already been resolved and thanks for sharing the solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others", I'll repost your solution in case you'd like to "Accept" the answer : )

---

[A local loop was detected]

Issue Symptom:

"As I am upgrading the hybrid exchange server 2010 to hybrid exchange server 2016.
HCW was successful, receive and send connector seem to be fine on the exchange 2016.

First I could not send an email from @mycompany.com to external email (@gmail.com) after updating the TlsCertificateName on the Default Frontend Ex2016 from Receive connector Exchange 2016, now I am able to send out.

But I am not able to receive an external email e.g ******@gmail.com to ******@mycompany.com, from EAC message trace status: resolved and delivered, I checked the Queue Viewer on the Exchange 2016, the email was stuck in the queue with the last error: A local loop was detected."

Resolution:

"As I mentioned external outbound flow was fine only external inbound was stuck in the queue with the last error : A local loop was detected, that means something misconfigured on the send connectors specifically "Outbound to Office 365" which really depends on your organization / or configuration (such as MX record, DNS ect..)

In my case, I enabled SMTP service on the third party certificate (mail.mycompany.com) and reran the HCW with the Full Hybrid Configuration option which corrected my send connector "Outbound to Office 365" and successfully mail flows as expected."

Answer 2

Hi All and @Yuki Sun-MSFT

FYI, I thought I'd like to share my experience for someone who might have the same issue.

As I mentioned external outbound flow was fine only external inbound was stuck in the queue with the last error : A local loop was detected, that means something misconfigured on the send connectors specifically "Outbound to Office 365" which really depends on your organization / or configuration (such as MX record, DNS ect..)

In my case, I enabled SMTP service on the third party certificate (mail.mycompany.com) and reran the HCW with the Full Hybrid Configuration option which corrected my send connector "Outbound to Office 365" and successfully mail flows as expected.

Hope it helps someone.

Best Regards,

Answer 3

Hi @vdz ,

all @mycompany.com email is in Exchange Online (Office 365)

Are these mailboxes migrated to Exchange Online from Exchange on-prem? How about mailboxes newly created in cloud?
Is the MX record pointed Office 365?

Besides, in case it's an issue with the inbound connector, you can run the command similar like below to check the configurations of the inbound connector:

Make sure it's enabled with a valid certificate:

Get-InboundConnector "Inbound Connector for Contoso.com" | Format-List

---

If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".

Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Answer 4

Hi @Yuki Sun-MSFT

Please see the in-line answers

Are these mailboxes migrated to Exchange Online from Exchange on-prem? How about mailboxes newly created in cloud?

In the Office 365 portal there is no option for my domain @mycompany.com only @mycompany.onmicrosoft.com available, that is a long story we have not done completely the DNS record in Office 365 portal, and normally we create an email account on the on-prem then move to the cloud and we have been doing this for a long time.

Is the MX record pointed Office 365?

No, the MX record is pointed to the third-party mail filtering.

As per suggested, I ran this cmd
Get-InboundConnector "Inbound from de3c068f ...." | fl

and the TlsSenderCertificateName is the same as TlsCertificateName on the Default Frontend Ex2016 I mentioned earlier.

In addition, currently we have a coexistence Ex2010 and Ex2016, only one server faces internet at a time, so when I do a test on Ex2016 I changed the IP address of Ex2016 in the firewall so that it is connected to outside world that is how I find the current issue.

As speak the Ex2010 is internet facing, the mail flow is completely fine as expected.

Best Regards