Error 550 5.1.10 when sending from local smtp (hybrid) and no error when sending from OWA

Mr. Peterson 266 Reputation points

We have a hybrid setup where all mailboxes are located in EO, and exchange server runs in Hybrid mode with local SMTP.

We have no problems sending an e-mail to an address sample@Company portal .com (recipient is outside of our tenant), but when we send a mail from local SMTP on Exchange Server we get

> Remote Server returned '550 5.1.10 RESOLVER.ADR.RecipientNotFound; Recipient not found by SMTP address lookup'

"Undeliverable" mail generating server is Exchange Server, so it seems the mail doesn't even leave on-prem to EO, however I checked Hub Logging logs and found no errors.
What could be a reason of that mail failure?

Microsoft Exchange Online Management
Microsoft Exchange Online Management
Microsoft Exchange Online: A Microsoft email and calendaring hosted service.Management: The act or process of organizing, handling, directing or controlling something.
4,233 questions
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.
7,383 questions
Microsoft Exchange Hybrid Management
Microsoft Exchange Hybrid Management
Microsoft Exchange: Microsoft messaging and collaboration software.Hybrid Management: Organizing, handling, directing or controlling hybrid deployments.
1,908 questions
0 comments No comments
{count} votes

Accepted answer
  1. Andy David - MVP 142.7K Reputation points MVP

    is Sample@Company portal .com an account in your org?

    If so, then its one of two issues:

    1. There is no remote mailbox enabled for that account on the on-prem Exchange Server


    1. The remote routing address on the existing remote mailbox on-prem is set incorrectly.

1 additional answer

Sort by: Most helpful
  1. KyleXu-MSFT 26,211 Reputation points

    @Mr. Peterson

    In a hybrid organization, if you send email from Exchange on-premises, email will be sent from Exchange on-premises to the Internet directly.

    So, I would suggest you create a new send connector for Exchange on-premises: Create a Send connector in Exchange Server to send mail to the internet

    Then enter this external email address manually (Don't use auto-complete or reply old emails)

    If you still cannot send emails successfully, I would suggest you try to use Message Tracking Log to check which step has issue:

    Get-TransportService | Get-MessageTrackingLog -Sender -Recipients -MessageSubject "subject" -Start 09/22/2022 -End 09/24/2022  

    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.