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Zakon's avatar
Zakon
Copper Contributor
Jan 26, 2023

Exchange hybrid - on-premise mailbox issue

Hi Guys,

 

I have a problem with mailbox that is located in on-premise Exchange 2019. I'm using hybrid mode with 99% mailboxes located in EXO. Let's name this mailbox: "Mailbox1".

 

Mailbox1 have 4 SMTP addresses. 3 of them are working correctly, only 1 is not working- mails sent on this SMTP are not delivered with error:

: ‎550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient XXXXXXXXX not found by SMTP address lookup‎

While I'm sending mail from this specific SMTP mail is delivered correctly - reply on this message is also not delivered.

 

I have found some discussions that could be related to this issue. For example:

https://learn.microsoft.com/en-us/exchange/troubleshoot/email-delivery/on-premises-users-not-getting-emails-from-microsoft-365 

 

All my accepted domains in EXO are configured as Authoritative. But I'm not sure that this is the root cause of this issue because it's working with 3 others SMTP for same mailbox and also some other mailboxes from on-premise are working correctly(some- not, same issue as described).

 

Do you have any experience with issue similar to this one?

 

BR,

Zakon

 

exchange online
Exchange Server
hybrid
office 365

5 Replies

  • Deleted's avatar
    Deleted
    Feb 08, 2023

    Zakon 

    The bounce back is returned when the recipient address isn't available on the server where your MX is pointing to. 

    Please confirm if the 4 SMTP addresses on Mailbox 1 are of the same domain name. 

    Please confirm if there are other working mailboxes (Mailbox 2, mailbox 3) with address like the affected domain name on Mailbox 1

    I look forward to your response in order to advise further. 

  • Zakon's avatar
    Zakon
    Copper Contributor
    Jan 27, 2023
    @update

    There are 2 objects in cloud:
    1. MailUser without required SMTP address added
    2. MsolUser with all SMTP synced from on-premise

    I'm not sure why on-premise mailbox is synced to MsolUser instead of MailUser.
    Both ExchangeGuid for on-premise Mailbox and MailUser are same.

    Any ideas?
    • Dan_Snape's avatar
      Dan_Snape
      Bronze Contributor
      Jan 30, 2023
      Not sure that you have this correct. MSOLUser is the user in AAD (found using get-MsolUser cmdlet). The mail user should be the same user but found in Exchange Online using the get-mailuser cmdlet. If you have TWO users found in AAD (and possibly EXO) with the same details, then you have a problem. Check the AAD Connect health to see if there are any sync errors. You might see an indication of duplicate addresses or user type mismatches
    • J_Tsai's avatar
      J_Tsai
      Copper Contributor
      Jan 28, 2023
      Do you see the SMTP address listed for the MailUser object in EOL? Run in EOL==> (Get-MailUser Mailbox1).EmailAddresses
      The address you're using have the correct email type "smtp:"?
      • Zakon's avatar
        Zakon
        Copper Contributor
        Jan 28, 2023
        SMTP addresses that were added into mailbox(on-premise) are sycned to MsolUser object instead of MailUser object in cloud. Any ideas how to fix that issue without excluding object from sync and deleting both objects in cloud?

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