Suddenly Same email Delived to both primery domain email and .onmicrosoft.com email

Question

Suddenly Same email Delived to both primery domain email and .onmicrosoft.com email

Kanchana Jayathilake 0

HI,

we suddenly noticed one of our user getting same email deliverd to both primery SMTP and .onmicrosoft.com email.in actual senarrio user only get one email but when we see the mail log we see it has deliverd to primery SMTP and second one has resolved.

my envirenment is one on-prem exchange which has migrated to M365 and two ads with azure connector.

221478

BR

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Answer 1

Yuki Sun-MSFT 41,336 Microsoft External Staff

Hi @Kanchana Jayathilake ,

Is the MX record of your domain pointing to your on-premises Exchange organization while the user mailbox you mentioned above is hosted in Exchange Online?

If both are true, it's actually the expected behavior. As in this scenario, inbound message will be delivered to on-premises Exchange server and then the on-premises Exchange server performs a lookup for each recipient using an on-premises global catalog server. When the global catalog lookup determines that the recipient's mailbox is located in the Exchange Online organization and has a hybrid routing address of ******@contoso.mail.onmicrosoft.com, it will deliver the email to either ******@contoso.mail.onmicrosoft.com account or the primary domain account.

Reference: Transport routing in Exchange hybrid deployments.

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Kanchana Jayathilake 0 Reputation points

2024-03-15T07:46:46.5433333+00:00

Hi @Yuki Sun-MSFT

Thank you for reply.no.my MX is only pointed to exchange online.ill attached the screenshot.same user was didnt had this error last week.actually users dosend know about this.we saw this in message trace.

user is on the cloud.

Thank you
Yuki Sun-MSFT 41,336 Reputation points Microsoft External Staff

2024-03-19T08:30:32.45+00:00

Hi @Kanchana Jayathilake ,

same user was didnt had this error last week

Any changes made to this user's mailbox recently? Especially in terms of email addresses.
Kanchana Jayathilake 0 Reputation points

2024-03-19T08:33:15.1533333+00:00

HI @Yuki Sun-MSFT

No..we have not done any changes.we dig into the matter littlebit further and found tha exchnage on-prem virsion not supported with cloud.can it be a problem?

BR

Kanchana
Yuki Sun-MSFT 41,336 Reputation points Microsoft External Staff

2024-03-27T06:34:51.08+00:00

Hi @Kanchana Jayathilake ,

As indicated in the image you shared, out-of-dated on-premise Exchange servers might lead to email delay or rejections issues. While in your case, the message can be delivered successfully. So, I don't think it's the cause of the resolved event we are discussing in this thread.

When it comes back to the issue we discussed, I tried searching a lot but so far cannot find more information stating this, but according to the document, the Resolved event means:

"The message was redirected to a new recipient address based on an Active Directory look up. When this event happens, the original recipient address is listed in a separate row in the message trace along with the final delivery status for the message."

So, taken in the round, my understanding is that it wouldn't affect the final delivery status of the message. It's just a redirect action occurred during the mail routing processing because the recipient has multiple addresses.

If you still have concerns on this, since it currently only occurs to the specific user, I'd suggest checking and comparing the email addresses settings of this user and a normal user to see if there's any difference.
Kanchana Jayathilake 0 Reputation points

2024-03-27T08:09:56.8566667+00:00

@Yuki Sun-MSFT

Thank you for your suggestion.we have requested update the exchange server anyway.i will do your method also and check if its the same.

BR

Kanchana

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Suddenly Same email Delived to both primery domain email and .onmicrosoft.com email

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