DBEB working randomly

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MikaelBohlin-3682 asked · Mar 02 at 08:41 AM

DBEB working randomly

DBEB in Exchange Online Protection should reject inbound emails to addresses not found in the internal directory. If I send an email to a made-up address (john.doe@mycompany.org) from an external mailbox, I do get a NDR saying 5.4.1 access denied. So far so good. But when I send an email that we deleted back in year 2011, from our internal AD and onprem Exchange, the email is accepted by the DBEB and processed by the MTA. The result gives an NDR as well, but with "not found in the smtp addressbook". Why is DBEB accepting a user that we deleted 10 years ago, a user that was deleted many years before AD Sync to Azure and the Exchange Hybrid setup? I assume there are something left in AD/Exchange, but where shall I look for it?

office-exchange-online-itpro office-exchange-server-mailflow

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joyceshen-MSFT · Mar 05 at 08:01 AM

Hi @MikaelBohlin-3682

Is there any update about your issue?

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joyceshen-MSFT · Mar 12 at 07:58 AM

Hi @MikaelBohlin-3682

Any progress so far?

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Answer 1 · 2021-03-03T03:02:34.007Z

joyceshen-MSFT answered · Mar 03 at 03:02 AM

Hi @MikaelBohlin-3682

According to your information above, the user is deleted before you configure Exchange hybrid and sync to cloud. And DBEB not working for this account.

DBEB block all messages sent to email addresses that aren’t present in Azure Active Directory.

Try using the commands below to see any result returned back about the user:

 Get-AzureADUser -ObjectId "testUpn@tenant.com"
 Get-Recipient -Identity <MailUserIdentity> | Format-List

Detailed information Manage mail users in standalone EOP

In addition, have you checked in onprem AD that the deleted user is not able to be found?

Could you please provide the complete NDR you received for that account?

Some further information about DBEB attached here as well: In Deployment: Directory Based Edge Blocking for Exchange Online Protection

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